1 J

X = 0 ; Y = NH2, NMe,, SEt, or SPh X = S; Y = NH2 or NMe2

R = H or Me

Synthesis and complexation of a tridentate organogallate ligand containing pyrazolyl and pyridylmethoxy donor groups

STEVEN J. RETTIG, ALAN STORR, JAMES TROTTER, AND KALEN UHRICH Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T 1Y6

Received March 26, 1984

STEVEN J. RETTIG, ALAN STORR, JAMES TROTTER, and KALEN UHRICH. Can. J. Chem. 62, 2783 (1984). The synthesis and complexation of the novel tridentate anionic organogallate ligands [Me2Ga(N,C3HR2){0CH2(Cs~4~)}]-

(where R = H or Me) have been investigated. The ligands, containing both pyrazolyl and pyridyl donor groups, have been incorporated into a variety of octahedral transition metal carbonyl compounds in a fac coordination mode. A tetrahedral nickel nitrosyl complex is also described and X-ray crystal structures of bis(pyridine-2-methanolatodimethylgallium) and [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-pyridylmethoxy)gaIlato-~2,0,N']tricarbonylrhenium(l) are reported. Crystals of bis(pyridine-2-methanolatodimethylgallium) are monoclinic, a = 16.716(2), b = 7.6513(6), c = 7.7591(8) A, P = 108.349(5)", Z = 2, space group C2/m. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.029 and R,,, = 0.032 for 809 reflections with I r 3u(I). The dimeric molecule has crystallographically imposed C2,, symmetry, the Ga atom having an irregular trigonal bipyramidal coordination geometry. Bond distances (correcte: for libration) are Ga-O(eq) = 1.939(3), Ga-O(ax) = 2.086(3), Ga-N(ax) = 2.276(3), and Ga-C(eq) = 1.981(4) A. Crystals of [dimethyl(3,5-dimethyl-I-pyrazolyl) (2-pyridylmeth0xy)gallato-N~,0,~~]tricarbon~l- rhenium(1) are monoclinic, space group P21/n, a = 9.7457(7), b = 36.991(3), c = 10.8821(8) A, P = 92.944(3)", Z = 8. The structure was solved by heavy-atom methods and was refined to 0.042 and R,,. = 0.047 for 5321 reflections. Each of the two crystallographically independent molecules displays the expected fac octahedral coordination geometry with Re-0 = 2.142(6) and 2.143(8), Re-N = 2.166(10)-2.194(8), and Re-CO = 1.89(2)-1.919(11) A.

STEVEN J. RETTIG, ALAN STORR, JAMES TROTTER et KALEN UHRICH. Can. J. Chem. 62, 2783 (1984). On a etudit la synthkse et la complexation des nouveaux ligands organogallates tridentates anioniques

[Me2Ga(N,C3HR2){0CH2(C5H4N)}]- dans lesquels R = H ou Me. On a incorporC les ligands contenant a la fois les groupes donneurs pyrazolyle et pyridyle dans une variCtC de composCs carbonylts octatdriques du mCtal de transition qui sont caracttrisCs par un mode de coordination fac. On dCcrit aussi un complexe tttrakdrique du nitrozyle de nickel et, utilisant la diffraction des rayons-X, on a dtterminC les structures cristallines du bis(pyridinemtthano1ato-2 dimCthylgallium) et du [dimCthyl(dimCthyl-3,5 pyrazolyl-l)(m&thoxy-2 pyridinyl) gallato-N2,0,N3]tricarbonylrhCnium(I). Les cristaux du bis(pyridinemCthano1ato-2 dimtthylgallium) sont monocliniques, a = 16,7 16(2), b = 7,65 13(6), c = 7,759 l(8) A, P = 108,349(5)", Z = 2, groupe d'espace C2/m. La structure a ttt rCsolue par les mtthodes conventionnelles aux atomes lourds et elle a CtC affinCe par la mCthode des moindres carrts (matrice entiere) jusqu'a des valeurs de R = 0,029 et R,. = 0.032 pour 809 rkflexions avec I r 3u(I). La molCcule dimkre posskde une symttrie cristallographique C2,, imposCe et la gtomCtrie de coordination de l'atome de Ga est bipyramidale trigonale irrCgulikre. Les longueurs des liaisons (corrigies pour la libration) sont: Ga-O(Cq) = 1,939(3), Ga-O(ax) = 2,086(3), Ga-N(ax) = 2,276(3) et Ga-C(Cq) = 1,981(4) A. Les cristaux du [dimtthyl(dimtthyl-3,5 pyrazolyl-l)(mtthoxy-2 pyridyl) gallato-~~~,N']tricarbonyIrh~nium(l) sont monocliniques, groupe d'espace P21/n, a = 9,7457(7), b = 36,991(3), c = 10,8821(8) A, P = 92,944(31°, Z = 8. La structure a ttt rtsolue par la mtthode des atomes lourds et elle a C t t affinCe jusqu'a des valeurs de R = 0,042 et R,.. pour 5321 rtflexions. Chacune des deux molCcules, qui sont cristallographiquement indtpendantes, posskde la gtomttrie de coordination attendue, fac octa- Cdrique, avec Re-0 = 2,142(6) et 2,143(8), Re-N = 2,166(10)-2,194(8) et Re-CO = 1,89(2)-1,919(11) A.

[Traduit par le journal]

Introduction r -

These ligands all contain a monofunctional donor pyrazolyl moiety in conjunction with a bifunctional donor system, both being attached to a dimethyl gallium grouping. The many novel aspects displayed by compounds containing these ligands prompted us to extend our investigations in this area to include a pyridyl "aromatic" ring in the ligand system to give 2.

Unsymmetrical uninegative tridentate chelating organo- gallate ligands, 1, have been the subject of a number of recent publications (ref. 1 and references therein). - L- =

The new ligands have yielded a variety of transition metal complexes and one of these, LRe(CO),, has been characterized by X-ray crystallographic analysis.

RwR /"-"\

Me2Ga\

O ' - @ - -

Experimental

2

Air-sensitive materials were handled in a glove box under an atrno- sphere of oxygen-free dry nitrogen, in a nitrogen-blanketed apparatus or on a high-vacuum line. Tetrahydrofuran (THF) was dried by re- fluxing over Na/benzophenone and was used immediately following distillation. Benzene was dried by refluxing over molten potassium followed by distillation. Sodium pyrazolide and sodium 3,5-dimethyl-

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CAN. J . CHEM. VOL. 62 . 1984

Calcd. (%) Found (%) VCO(VNO) cm-' *

M R T C H N C H N

Mn Me (Co), 43.48 4.33 9.51 43.56 4.37 9.77 2035,1943,1908 Re Me (CO), 33.52 3.34 7.33 33.92 3.52 7.34 2028, 1924, 1898 Ni Me NO 39.86 4.89 14.30 39.88 4.92 14.00 (1783) Mo H ( C O ) ~ ( ~ ~ - C ~ H S ) 41.06 4.27 8.98 41.07 4.17 8.86 1942, 1855 Mo H (C0)2(q3-C4H7) 42.36 4.60 8.71 42.52 4.62 8.55 1938, 1853

*Measured in cyclohexane.

FIG. 1. 400 MHz 'H nmr spectrum of [Me2GaOCHz(CsH4N)] in C6D6.

pyrazolide were prepared by reacting sodium hydride (Alfa) with the appropriate pyrazole (K and K Laboratories) in THF. Trimethyl gal- lium (2), Ni(N0)I (3), Mn(CO)sBr (4), and [Re(C0)4C1]2 (5) were prepared as previously described. Ally1 bromide and 2-methylallyl chloride were distilled before use. (MeCN),Mo(CO), was prepared from Mo(CO)~ (Strem) by a standard route (6). Pyridyl-2-methanol (Aldrich) was used as supplied.

Preparation of [Me2GaOCHz(C5HY)h Me3Ga + HOCH2(C5H4N) + (1/2)[Me2GaOCH2(C5H4N)]2 + MeH

To a solution of trimethylgallium (2.42 g, 21.1 mmol) in THF was added pyridine-2-methanol (2.30 g, 21.1 mmol) in the same solvent. The reaction mixture was refluxed for 24 h and the solvent removed under vacuum. The solid obtained was extracted with benzene. The resulting solution afforded white needles of the desired product upon slow evaporation of the solvent. Yield -85%. Anal, calcd. for [Me2GaOCH2(C5H4N)]2: C 46.22, H 5.82, N 6.74; found: C 45.87, H 6.00, N 6.56. The 'H nmr spectrum of the product is shown in Fig. 1.

Preparation of the ligand L- Na+(N2C3HR2)- + Me3Ga + Na+[Me3Ga(N2C3HR2)]-

Na'[Me,Ga(N2C3HR2)]- + HOCH2(CsH4N) + Na'L- + CH4 Typically, trimethylgallium (2.26 g, 19.7 mmol) in 50 mLTHF was

added to sodium 3,s-dimethylpyrazolide (R = Me) (2.33 g, 19.7 mmol) in 50 mL of the same solvent. After stirring the solution at room temperature for approximately 1 h a 50 mL THF solution of pyridine-2-methanol (2.15 g, 19.7 mmol) was added and the reaction

mixture refluxed overnight. The solution was cooled and diluted to 250 mL in a standard flask. Aliquots of this standard solution were used in subsequent reactions.

Preparation of LM~I(CO)~ To a stirred solution of Mn(C0)5Br in THF (0.53 g, 1.97 mmol)

was added 25 mL THF solution of the ligand Na'L- (R = Me) (1.97 mmol). The reaction mixture was stirred overnight at room tem- perature and the solvent was then removed under vacuum. The orange residue was extracted with benzene and the solution filtered. The filtrate, on slow evaporation of the solvent, gave dark orange-brown crystals of the product in approximately 70% yield. Analytical, ir, and nmr data for this complex and those described below, are collected in Tables 1 and 2. The LRe(CO), complex was prepared similarly using the [Re(CO)4C1]2 dimer as starting material. The product was col- lected in -70% yield.

Preparation of LNi(N0) To a stirred solution of Ni(N0)I (0.83 g, 3.84 mmol) in 50 mL THF

was added 50 mL THF solution of Na+L- (R = Me) (3.94 mmol). The reaction mixture was stirred overnight at room temperature and the solvent was then removed under vacuum. The blue residue was extracted with benzene and recrystallization from this solvent afforded a deep blue microcrystalline product in -65% yield.

Preparation of NU+LMO(CO)~- solution To a stirred 50 mL THF solution of (MeCN),Mo(CO), (2.703 g,

8.92 mmol) was added 100 mL THF solution of Na+L- (R = H) (8.92 mmol). The resulting mixture was stirred overnight and the resultant orange-brown solution of Na+LMo(CO),- made up to 250 mL in a standard flask.

Preparation of L M O ( C O ) , ( ~ ~ - C ~ H ~ ) To a 50 mL solution of Na+LMo(CO),- (R = H) (1.78 mmol) was

added an excess of ally1 bromide. The mixture was stirred for 24 h and the solvent removed under vacuum. Recrystallization of the brown residue from benzene yielded waxy orange crystals of the product in -65% yield.

'The L M O ( C O ) ~ ( ~ ~ - C ~ H , ) complex was prepared similarly, substi- tuting 2-methylallyl chloride as one of the reactants. The product was obtained as orange crystals in -70% yield.

X-ray crystallographic analyses [Me2GaOCH2(C5H4N)J A crystal bounded by the six faces (followed by their distances in

mm from a common origin): *(O 0 I), 0.188, 2 (1 1 O), 0.094, ?(-I 1 O), 0.094 was mounted in a general orientation. Unit-cell parameters were refined by least-squares on 2 sin 0/X values for 25 reflections (20 = 35-44") measured on a diffractometer with Mo-Ka

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TABLE 2. 'H nmr data for ~ e ~ ~ a ' MT complexes in C6D6 solution

T*

M R T -OCH2- H4 R "allyl" Ga-Me - - - -

Ni Me NO 5.33 s 3.98 s 7.06 s, 7.92 s 9.83 s Re Me (C0)3 A = 5 . 0 3 , B = 5 . 3 5 4.43s 7 . 5 7 ~ , 8 . 1 5 s 9.79 s, 10.26 s

(J = 16 Hz) Mnt Me (Co), A = 4.71, B = 4.85 4.17 s 7.42 s, 7.88 s 10.26 s, 10.38 s

( J = 16 Hz) Mo H ( C O ) ~ ( ~ ~ - C , H ~ ) A = 5.38, B = 5.44 4.05 t 2.24 d, 3.01 d 8.32 d, 8.50 d (H ,,,,,, J = 10 Hz) 10.10 s, 10.56 s

( J = 15 Hz) 6.64 d, 6.65 d (H,,, J = 6 Hz) 6.08 tt (H .,,,., J = 6, 10 Hz)

Mo H ( C O ) ~ ( ~ ~ - C ~ H ~ ) A = 5.15, B = 5.43 3.94 t 2.13 d, 2.98 d 8.29 s (ally1 Me) 9.88 s, 10.77 s ( J = 16 Hz) 8.37 s, 8.52 s (H ,,,3,,)

6.81 d, 6.91 d (H ,,,, J = 4 Hz)

* r values refer to (rCgH6 = 2.84 ppm). s = singlet, d = doublet, t = triplet, tt = triplet of triplets. t Measured in acetone-d6; T values refer to (r,,,,,., = 7.89 ppm).

Radiation (A(Kcxl) = 0.70930, A(Kaz) = 0.71359 A). Crystal data at 22°C are: C I ~ H z ~ G ~ z N z O ~ fw = 207.91 Monoclinic, a = 16.716(2), b = 7.6513(6), c = 7.7591(8) A, P = 108.349(5)", V = 941.9(2) A', Z = 2, PC = 1.466 g ~ m - ~ , F (000 ) = 424, p,(Mo-Ka) = 238.57 cm-I. Absent reflections: hkl, h + kodd, space group C2/m (C,,,, No. 12) frorn structure analysis.

Intensities were measured with graphite-monochromated Mo-Kcx radiation on an Enraf-Nonius CAD4-F diffractometer. An w-20 scan at 1.26- 10.06" min-I over a range of (0.60 + 0.35 tan 0) degrees in w (extended by 25% on both sides for background measurement) was employed. Data were measured to 20 = 60". The intensities of three check reflections, measured every 3600 s throughout the data col- lection, remained constant to within 2%. After data reduction,' an absorption correction was applied using the Gaussian integration method (7, 8). Transmission factors ranged from 0.439 to 0.652 for 96 integration points. Of the 1460 independent reflections measured, 809 (55.4%) had intensities greater than 3u(I) above background where u2(I) = S + 2B + (0.04(S - B))' with S = scan count and B = normalized background count.

The centrosymmetric space group C2/m was indicated by the E- statistics. The coordinates of the Ga atom were determined from the Patterson function and those of the remaining atoms from subsequent difference syntheses. The non-hydrogen atoms were refined with an- isotropic thermal parameters and the hydrogen atoms with isotropic thermal parameters. The scattering factors of ref. 9 were used for non-hydrogen atoms and those of ref. 10 for hydrogen atoms. Anom- alous scattering factors from ref. 11 were used for the Ga atoms. The weighting scheme, w = l /uZ(F) where u2(F) is derived frorn the

reviously defined u2(1), gave uniform average values of w(lFo( - F,1)' over ranges of both IFoI and sin 0/A and was employed in the P final stages of refinement. Reflections with I < 3u(I) were not

' The computer programs used include locally written programs for data processing and locally modified versions of the following: ORFLS, full-matrix least-squares, and ORFFE, function and errors, by W. R. Busing, K. 0 . Martin, and H. A. Levy; FORDAP, Patterson and Fourier syntheses, by A. Zalkin; ORTEP 11, illustrations, by C. K. Johnson.

included in the refinement. Convergence was reached at R = 0.029 and R , = 0.032 for 809 reflections with I r 3u(I). For all 1460 reflections R = 0.078. The function minimized was Z w ( ( ~ ~ l - IF,^)', R = ZllFol - IF,II/ZIF~~ and R , = (Zw(lFoI - I F , ~ ) ' / Z W ~ F ~ ~ ~ ) " ~ .

On the final cycle of refinement the mean and maximum parameter shifts corresponded to 0.04 and 0.27u, respectively. The mean error in an observation of unit weight was 1.402. A final difference map showed maximum fluctuations of -0.81 to $0.67 e A-3 near Ga and 20.17 e A-3 elsewhere. The final positional and thermal parameters appear in Tables 3 and 7,' respectively. Measured and calculated structure factors have been placed in the Depository of Unpublished Data.'

The ellipsoids of thermal motion for the non-hydrogen atoms are shown in Fig. 5. The thermal motion has been analysed in terms of the rigid-body modes of translation, libration, and screw motion (12). The rms standard error in the temperature factors uUij (derived from the least-squares analysis) is 0.0027 A'. Analysis of the entire molecule (rms AU,, = 0.007 1 A') showed significant independent motion of the Me2Ga units. Fragment consisting of the pyridine ring plus C(6) and the Ga coordinati~n~group were separately analysed (rms AUij = 0.0026 and 0.0020 A'). The appropriate bond distances have been corrected for libration (12, 13), using shape parameters q 2 of 0.08 for all atoms involved. Corrected bond lengths appear in Table 4 along with the uncorrected values; corrected bond angles do not differ by more than l o from the uncorrected values given in Table 5. Intra- annular torsion angles defining the conformations of chelate rings are listed in Table 6 for [Me2Ga(N2C5H7)0CH2(C5H4N)]Re(CO),. Bond lengths and angles involving hydrogen and a complete listing of tor- sion angles (Tables 8- 10) are included as supplementary material.

[M~~G~(N~C~H~)~CHZ(C~H$I)]R~(CO)~ Experimental details are as above except where noted. The bound-

ing planes of the crystal used for data collection were: *(O 1 O),

'The structure factor table, Table 7 (anisotropic thermal parame- ters) and other material mentioned in the text are available, at a nominal charge, from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Ont., Canada KIA OS2.

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2786 CAN. J . CHEM. VOL. 62. 1984

TABLE 3. Final positional (fractional X lo4, Re and Ga X lo5, H x 10') and isotropic thermal parameters (U X 10' A') with estimated standard deviations in parentheses*

Atom x Y z UCq/U,,, Atom x Y z ucq/Ut,c,

[Me2GaOCH2(C5H,N)]2 Ga 424 17(3) 50000 31230(5) 60 C(7) 41 18(3) 2750(6) 1839(7) 95 0 4459(2) 5000 5711(4) 81 H(2) 234(3) 500 679(7) 68(13) N 2945(2) 5000 3484(4) 64 H(3) 99(4) 500 470(9) 108(18) (31) 2977(3) 5000 5215(5) 63 H(4) 1 OO(4) 500 189(7) 81(16) c(2) 2250(4) 5000 5723(8) 89 H(5) 2 16(3) 500 94(7) 77(12) c(3) 1492(4) 5000 4391(9) 103 H(6) 389(2) 393(4) 735(4) 79(9) (74) 1456(4) 5000 2614(8) 91 H(7a) 36 l(2) 240(5) 138(5) 96(13) c(5) 2 189(3) 5000 2203(7) 78 H(7b) 445(3) 252(6) 123(8) 123(17) c(6) 385 l(3) 5000 6557(5) 69 H(7c) 438(4) 208(11) 294(12) 223(37)

[Me2Ga(N~C5H7){0CH2(C5H4N)}IRe(CO), Re(1) 34676(4) 28863(1) 45596(3) 39 C(8) 4149(13) 4058(3) 4201(10) 58 Re(2) 63365(5) 9719(1) 37458(4) 52 (39) 327 l(10) 3770(3) 4249(9) 46 Ga(1) 68156(1 1) 31717(3) 44757(10) 47 C(10) 4134(10) 2813(3) 1901(9) 41 Ga(2) 81 173(16) 3474(4) 20287(13) 67 C(11) 4038(11) 281 l(3) 617(10) 51 O(1) 5464(7) 2823(2) 3852(7) 49 C(12) 2814(13) 2887(3) 25(10) 60 o(2) 470(8) 2966(3) 5220(9) 84 C(13) 1702(12) 298 l(3) 707(11) 59 O(3) 2908(11) 2077(3) 4715(10) 88 C(14) 1879(10) 2978(3) 1973(10) 50 O(4) 4195(10) 2846(3) 7330(8) 89 C(15) 6846(14) 4092(4) 4325(14) 79 O(5) 7750(8) 856(2) 2353(6) 56 C(16) 1727(13) 3780(4) 4204(12) 68 O(6) 4586(12) 1215(4) 5847(12) 128 C(17) 5237(14) 1107(4) 5048(13) 77 O(7) 5726(12) 1737(3) 2774(10) 99 C(18) 5938(14) 1444(4) 3117(11) 70 O(8) 3644(12) 740(4) 2398(12) 123 C(19) 4693(16) 81 l(4) 2879(15) 86 N(1) 5376(8) 3555(2) 4395(8) 46 C(20) 664 1 (20) 169(5) 895(16) 110 N(2) 3988(8) 3459(2) 4366(7) 41 C(21) 10076(18) 266(5) 1762(15) 103 N(3) 3087(8) 2897(2) 2571(7) 44 C(22) 8829(15) 1108(3) 2378(10) 64 N(4) 7731(12) 218(3) 3734(9) 67 C(23) 8019(19) -82(4) 4375(16) 92 N(5) 691 l(11) 440(3) 4428(9) 62 C(24) 7329(18) -70(4) 5480(14) 86 N(6) 8360(9) 1134(2) 4535(7) 45 C(25) 6675(14) 259(4) 5487(12) 72 c(1) 1620(12) 2949(3) 4974(11) 60 C(26) 9319(11) 1180(3) 3701(9) 48 c(2) 3140(11) 2380(3) 4633(10) 50 C(27) 10641(12) 1289(3) 4055(11) 61 (73) 395 l(11) 2869(4) 6290(10) 60 C(28) 10974(12) 1360(3) 5270(11) 61 c(4) 73 16(11) 3089(3) 6210(10) 55 C(29) 10002(12) 1302(3) 61 12(10) 57 c(5) 8127(12) 3245(4) 3196(11) 71 C(30) 8704(12) 1197(3) 5734(9) 49 C(6) 5423(11) 2692(3) 2627(10) 52 C(3 1) 8901(26) -384(5) 3902(21) 135 (77) 5459(13) 391 l(3) 4300(10) 56 C(32) 5869(22) 403(5) 6489(15) 113

* U,, = (113) trace (Ud,,,), coordinates having no esd's are fixed.

0.1 13, ?(O 0 I), 0.250, ?(1 0 O), 0.263 mm. Reflections employed in the refinement of the unit-cell parameters had 20 = 35-46". Crystal data are as follows: C14H15GaN304Re fw = 545.21 Monoclinic, a = 9.7457(7), b = 36.991(3), c = 10.8821(8) A, P = 92.944(3)", V = 3917.8(5) p, Z = 8, pc = 1.849 g ~ m - ~ , F(000) = 2064, p,(Mo-Ka) = 76.47 cm-I. Absent reflections: OkO, k odd, and h01, h + 1 odd, unique!y indicate the space group P2,ln (non- standard setting of P2,/c, C,,,, No. 14, equivalent positions: ? ( x , y, z; 112 - x , 112 + y, 112 - z)).

An w scan at 1.44- 10.06" min-' over a range of (0.65 + 0.35 tan

(Thornley-Nelmes definition of mosaic anisotropy with a Lorentzian distribution) was applied (15- 17). The final value of g was 4 3 3 ) X

lo4. The structure was refined to 0.042 and R,,, = 0.047 for 5321 reflections. The mean and maximum parameter shifts on the final cycle of refinement corresponded to 0.06 and 0.40 a , respectively. The mean error in an observation of unit weight was 1.918. A final difference map showed maximum fluctuations of k2.6 e A-hear Re. Calculated coordinates and thermal parameters for hydrogen atoms (Table 1 I) are included as deposited material. The two independent molecules are shown in Fig. 6.

0)" in w was employed. Of 8952 independent reflections measured (to 20 = S o ) , 5321 (59.4%) had intensities greater than 3u(I) above Results and discussion background. The intensities of the three check reflections remained Several recent publications have discussed a variety of metal constant to within 2.5%. Data were corrected for absorption using the complexes with multidentate ligand systems containing both analytical method (7, 14), transmission factors ranging from 0.057 to pyridyl and pyrazolyl donor functions (18, 19). It has been 0.199. concluded that pyrazolyl has weaker IT-acceptor capabilities

The structure was solved by conventional heavy-atom methods, the (20) but stronger a-donor properties than pyridine (18). The coordinates of the Re and Ga atoms being determined from the Pat- terson function and those of the remaining non-hydrogen atoms from present study extends our work in the area of unsymmetrical subsequent difference maps. All non-hydrogen atoms were refined uninegative tridentate organogallate ligands to include ligand with anisotropic thermal parameters and hydrogen atoms were Systems incorporating both a ~ ~ r a z o l ~ l and a Pyridyl donor included as fixed atoms in idealized positions (C(sp')--H = 0.97 and function. A variety of transition metal complexes bearing these C(sp3)-H = 0.98 A). An isotropic Type I extinction correction ligands has been characterized by the usual sporting physical

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TABLE 4. Bond lengths (A) with estimated standard deviations in parentheses

Length Length

Bond Uncorr. Corr. Bond Uncorr. Corr.

methods, and one of them has been further probed by X-ray crystallographic techniques.

The reactivity of pyridyl-2-methanol towards trimethyl- gallium was first investigated to confirm the expected methane elimination reaction. The product from this reaction, "[Me2GaOCH2(C5H4N)]", was shown to be monomeric in the gas phase, its mass spectrum displaying a weak monomer par- ent ion (P') signal and a very strong P - Me' signal. Similar dimethylgallium systems have been shown to be associated in the solid state (21, 22) and an X-ray crystal structure of the present pyridyl complex again demonstrated the dimerization of the monomer units via a four-membered [-Ga-0-l2 ring, each gallium having a distorted trigonal bipyramidal arrangement. It is interesting to compare the Ga-N bond lengths in the three complexes [Me2GaOCH2(C5H4N)I2, [Me2NCH2CHz0GaMe2l2 (22), and [Me2NCH2CH20GaH2]2 (22). The pyridyl complex is comparable with the dihydride (Ga-N = 2.276(3) and 2.279(3) A respectively), both bonds being considerably shorter than in the [Me2NCH2CH2- 0GaMe212 dimer (Ga-N = 2.471(4) A) where severe steric interactions between the "NMe," and "GaMe," moieties lead to bond lengthening.

The 'H nmr of the pyridyl complex in C6D6 solution (Fig. 1) shows sharp singlets for both the "GaMe," protons and the -OCH2- methylene protons. The spectrum is consistent with an overall planar structure for the monomer in dilute solution with the two GaMe groups and the two methylene protons lying above and below this plane.

The synthesis of the ligands Na'L-, 2, proceeded smoothly as did the subsequent reactions to yield the transition metal complexes listed in Tables 1 and 2. Analysis of mass spectral, ir, and 'H nmr data points to monomeric structures for the whole range of complexes studied. An octahedral structure is proposed for the manganese, rhenium, and molybdenum com- pounds with the tridentate gallate ligand occupying three facial positions. This arrangement has been proven conclusively for the LRe(C0)3 complex by a crystal structure determination (see below). The LNi(N0) complex is believed to possess a tetra- hedral transition metal centre although fluxional behaviour in solution at room temperature must be operative to explain the 'H nmr results for this compound.

Infrared spectra The ir spectral data reported in Table 1 for the octahedral

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TABLE 5. Bond angles (deg) with estimated standard deviations in parentheses*

Bonds Angle (deg) Bonds Angle (deg)

- *Here and elsewhere primed and double-primed atoms have coordinates related to those in

Table 3 Q the symmetry operations 1 - x , 1 - y, 1 - z and x , 1 - y, z, respectively.

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RETTIG ET AL.

I T \

FIG. 2. 100 MHz 'H nmr spectrum of [Me2Ga(NzC5H7){OCH~(C5H4N)}IRe(CO)~ in C6D6.

FIG. 3 . 100 MHz 'H nmr spectrum of [Me2Ga(N2C5H7){0CH2(CsH4N)}]NiN0 in C6D6.

TABLE 6 . Intra-annular torsion angles (deg) for [Me2Ga(~2C5H7){0C~2(C5H4N)}]Re(C0)~ with

standard deviations in parentheses

Atoms Value (deg)

complexes are consistent with a fac tridentate gallate ligand in these molecules. Thus, the tricarbonyl complexes give three strong bands in the vco region of the spectrum indicative of a facial arrangement of these ligands (23). The molybdenum dicarbonyl "allyl" complexes both show two strong vco bands, indicative of a cis arrangement of the CO ligands. These data, together with our studies on related complexes (24-26) and the 'H nmr data reported below, confirm a facial tridentate gallate ligand in these compounds. Comparison of the ir data of the pyridyl complexes (Table 1) with that of the corresponding complexes incorporating aminoalcohol moieties (1, R = H and Me, X = 0 , Y = NH2 or NMe2) (24) reflects the n-acidity of the pyridyl ring. Thus the frequencies for the pyridyl complex- es are consistently -10 cm-' higher than those for the com- plexes in ref. 24, suggestive of weaker back-bonding to the ancillary ligands in the present complexes due to competitive back-bonding to the n-system of the pyridyl ring.

'H nmr sDectra selected 'H nmr data for the transition metal complexes are

compiled in Table 2 and representative spectra are shown in Figs. 2-4. The 'H nmr spectra for the tricarbonyl species are consistent with the proposed facial arrangement o f the gallate ligand. Thus the Ga-Me groups appear as two singlets and the -OCH2-- methylene protons as an AB quartet (Fig. 2). A

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FIG. 4. 400 MHz 'H nmr spectrum of [MeZGa(N2C5H7){0CHI(CSH4N)}]Mo(CO)7(T3-C~7) in C6D6.

FIG. 5. Stereoscopic view of [Me2GaOCH2(C~H4N)]~; 50% probability thermal ellipsoids are shown for the non-hydrogen atoms. Hydrogen atoms have been assigned artificially small thermal parameters for the sake of clarity.

meridional arrangement of the gallate ligand, on the other hand, would most probably lead to equivalent Ga-Me groups and equivalent methylene protons and hence singlets in these regions of the spectra. Interestingly the room temperature 'H nmr spectrum of the LNi(N0) complex displays singlets for both of these groupings (see Fig. 3). This result would suggest a square planar arrangement around the Ni centre with a pseudo-meridional gallate ligand. However, the unlikelihood of a square planar arrangement for this complex in light of previous studies which have shown that square planar {MNO) '~

complexes should have an M-N-0 bond angle of 120" (27, 28) (contrary to the linear M-N-0 grouping suggested by the observed ir results) led us to suspect that a fluxional process was responsible for the observed room temperature spectrum. The closely related [Me2Ga(N2C3H3)(0CH,CHfiMe2)]Ni(NO) complex has been shown to be fluxional in solution and to have a tetrahedral Ni centre in the solid state (29). On cooling a solution of the above LNi(N0) pyridyl complex to -85OC a marked broadening of both the -GaMe2 and -OCH,- sin- glets was observed, indicative of a slowing down of the flux-

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