1387-7003/99/$ - see front matter q 1999 Elsevier Science S.A. All rights reserved.PII S1387- 7003 (99 )00026 -X

Tuesday Mar 30 11:26 AM StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications) Article: 164

Inorganic Chemistry Communications 2 (1999) 121–123

[Ru(CO)(CH3CO2)(tpa)]ClO4PC6H5CH3

(tpastris(2-pyridylmethyl)amine), the first ruthenium carbonylcomplex of tpa

Li Xu, Yoichi Sasaki *Division of Chemistry, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan

Received 19 February 1999

Abstract

The reaction of dodecacarbonyltriruthenium with tris(2-pyridylmethyl)ammonium perchlorate (tpaP3HClO4), in the presence of aceticacid, afforded a new ruthenium complex of tpa, [Ru(CO)(CH3CO2)(tpa)]ClO4PC6H5CH3 (1). Compound 1 has been characterized byX-ray structural analysis, IR and 1H NMR spectra. q 1999 Elsevier Science S.A. All rights reserved.

Keywords: Ruthenium complexes; Polypyridyl complexes; Carboxylate complexes; Carbonyl complexes

Tris(2-pyridylmethyl)amine (tpa) and its derivativeshave been widely used as a tripodal tetradentate ligand todesign a variety of metalloenzyme model and related com-plexes [1–9], especially those containing iron [1–4] andcopper [5]. As a congener of iron, ruthenium complexescontaining tpa have received considerable attention. Severalcomplexes including [Ru2(m-O)(m-CH3CO2)(tpa)2]

3q,[Ru2(m-O)Cl2(tpa)2]

2q, [RuCl2(tpa)]q, [RuCl(dmso)-(tpa)]q and [Ru2(m-Cl)2(tpa)2]

2q, have been synthesizedand structurally characterized [10–13]. However, to ourknowledge, no ruthenium carbonyl complex of tpa has beenreported to date. The first carbonyl complex of tpa has beenreported recently for molybdenum(0), i.e. Mo(CO)3(tpa),where tpa acts as a tridentate ligand with the free pyridyl armundergoing rapid exchange with the coordinated pyridyl rings[14]. Herein, we wish to report on the synthesis and char-acterization of a new carbonyl ruthenium(II) complex of tpa,[Ru(CO)(CH3CO2)(tpa)]ClO4PC6H5CH3 (1). The newcomplex 1 represents, to our knowledge, the first example ofruthenium carboxylate complex containing single carbonylligand, although several oxo-bridged trinuclear rutheniumcarboxylate complexes containing single terminal carbonyl,are known [15–17]. It should be noted that synthesis ofmonocarbonyl polypyridyl complexes of ruthenium has beenthe subject of several studies as both precursors in the syn-

* Corresponding author. Tel.: q81-11-706-3817; Fax: q81-11-706-3447;E-mail: ysasaki@science.hokudai.ac.jp

thesis of Ru(II) complexes and catalysts in the multi-electronreduction of carbon dioxide [18,19].

Compound 1 was prepared as yellow crystals from thereaction of dodecacarbonyltriruthenium, tris(2-pyridyl-methyl)ammonium perchlorate [20] and acetic acid in tol-uene 1. Both the dicarbonyl and the diacetate complexes,Ru(CO)2(tpa) and Ru(CH3CO2)(tpa), were not found inthe reaction mixture. It has been well established that thereaction of dodecacarbonyltriruthenium and acetic acid intoluene afforded the insoluble polymer, [Ru2(CO)4-(CH3CO2)2]n [21]. The reaction of [Ru2(CO)4(CH3-CO2)2]n and 2,29-bipyridine (bpy) was reported to producea mononuclear ruthenium(II) complex, [Ru(CO)2-(CH3CO2)2(bpy)], on the basis of spectroscopic data [22].However, compound 1 was not obtained from the reaction of

1 Preparation of 1. A suspension of tpaP3HClO4 (0.18 g, 0.3 mmol) (Cau-tion: perchlorate salts of metal complexes with organic ligands are poten-tially explosive), Ru3(CO)12 (0.065 g, 0.1 mmol) and acetic acid (1 ml)in toluene was heated under reflux for 4 h under argon atmosphere. Thesuspension changed to a red–orange and then yellow solution after 10 min.The resulting solution was cooled to room temperature and was allowed tostand in a refrigerator overnight to give thin yellow plate crystals of 1. Yield,0.03 g (17%). Anal. Found: C, 49.76; H, 4.25; N, 8.22. Calc. forC28H29N4RuO7Cl: C, 50.14; H, 4.36; N, 8.36%. lmax/nm (in CH2Cl2): 250,385. IR (KBr (cmy1)): n(CO), 1938; nas(CO2), 1620. 1H NMR (CD2Cl2)d: 8.92 (1H, d, ortho py-H trans to acetate), 8.67 (2H, d, ortho py-H cis toacetate), 7.15–7.55 (11.5H, m, py-H and C6H5CH3), 5.37 (2H, s, pyridyl-methyl protons trans to acetate), 5.20 (4H, d, pyridylmethyl protons cis toacetate), 1.78 (3H, s, CH3CO2), 1.26 (1.5H, s, C6H5CH3).

L. Xu, Y. Sasaki / Inorganic Chemistry Communications 2 (1999) 121–123122

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Fig. 1. ORTEP drawing of the cation of 1, [Ru(CO)(CH3CO2)(tpa)]q,with 50% thermal ellipsoids. Selected bond lengths (A) and angles (8): Ru–Cl, 1.81(1); Ru–O2, 2.086(8); Ru–N1, 2.132(8); Ru–N2, 2.08(1); Ru–N3, 2.062(9); Ru–N4, 2.064(9); C1–Ru–O2, 96.7(4); C1–Ru–N1,177.0(4); C1–Ru–N4, 94.4(4); O2–Ru–N4, 168.6(3); N2–Ru–N3,162.5(4); O2–Ru–N1, 86.2(3); N1–Ru–N4, 82.7(3).

[Ru2(CO)4(CH3CO2)2]n and tpa, suggesting that the poly-mer may not be an intermediate in the formation of 1.

Complex 1 has been characterized by X-ray crystallogra-phy 2. Fig. 1 shows the structure of the cation of 1,[Ru(CO)(CH3CO2)(tpa)]q. The cation contains an octa-hedrally coordinated Ru(II) ion with two axial sites occupiedby the pyridine rings (N2 and N3) trans to each other andfour equatorial ones by the tertiary amine (N1), the otherpyridyl arm (N4), a carbonyl and an acetate group. Thestructure has an ideal mirror symmetry with the mirror planedefined by the RuN(1)C(16)C(17)N(4) five-memberedring. The acetate group slightly deviates from the plane. TheCs symmetry exists also in solution as indicated by the 1HNMR spectrum described below. The N2–Ru–N3 angle is162.5(4)8, indicating that the octahedron is distorted. Thefact that the carbonyl group occupies the site trans rather thancis to the N1 (tertiary amine) atom (N1–Ru–C1, 177.0(4)8)may be a consequence of strong Ru(II)™CO back donationas indicated by the unusually short Ru–C bond (1.81 A) andlow CO stretching frequency (1938 cmy1). The site trans toCO prefers to take s or weak p donors, i.e. tertiary nitrogenrather than pyridyl nitrogen. The Ru–C(CO) bond lengthis slightly shorter than those in [Ru3(m3-O)(m-CH3-CO2)6(mbpyq)2(CO)]2q (mbpyqsN-methyl-4,49-bi-pyridinium ion) (1.84(2) A) [17] and in [Ru(CO)-(CH2OH)(bpy)2]

q (1.85(1) A) [18]. As a consequence,the C–O bond length in 1 (1.17(1) A) is longer than thosein these two examples (1.13(3) and 1.11(1) A, respec-tively). In contrast to the structural data, the CO stretchingfrequency in 1 is similar to that in the triruthenium complex(1940 cmy1) and slightly shorter than that in the bpy com-plex (1925 cmy1). The Ru–N1(amine) distance (2.132(8)A) is significantly longer than the remaining Ru–N(pyridyl)distances (2.07(1) A) probably due to both the trans effectof CO and the absence of the d–pp bond. It should be notedthat the former is similar to the Ru–N(pyridyl) distance(2.125(6) A) trans to the CO group in [Ru(CO)-(CH2OH)(bpy)2]

q [18]. The Ru–N(pyridyl) bond lengthsin 1 are similar to those cis to the CO and CH2OH groups in[Ru(CO)(CH2OH)(bpy)2]

q [18]. The acetate group is cisto the tertiary amine nitrogen with the Ru–O distance of

2 Crystal data for [Ru(CO)(CH3CO2)(tpa)]ClO4PC6H5CH3 (1): Ms670.78, monoclinic, space group P21/c (No. 14), as9.178(4),bs16.562(5), cs19.397(5) A, bs98.63(3), Vs2915(1) A3, Zs4,rcalcs1.53 g cmy3, F(000)s1368, m(Mo Ka)s6.81 cmy1. Data werecollected on a Rigaku AFC-5R diffractometer withgraphite-monochromatedMo Ka at radiation (ls0.71073 A) at room temperature (238C). Cellconstants and an orientation matrix for data collection were obtained froma least-squares refinement using setting angles of 25 carefully centeredreflections. Data were corrected for Lorentz and polarization effects and/oran empirical absorption correction using the program DIFABS. The structurewas solved by heavy-atom Patterson methods and expanded using Fouriertechniques. Non-hydrogen atoms were refined anisotropically. The finalcycle of full-matrix least-squares refinement was based on 2469 observedreflections (I)3s(I)) and converged with Rs0.064 and Rws0.054. Theminimized function was Sw(NFoNyNFcN)2, where ws[sc

2(Fo)qp2Fo2/

4]y1.

2.086(8) A, which is close to those in [Ru3(m3-O)(m-CH3CO2)6(mbpyq)2(CO)]2q (2.07(1) A) [17] and[Ru2(m-O)(m-CH3CO2)(tpa)2]

3q (2.085(7) A) [10].The 1H NMR spectrum of 1 in CD2Cl2 corresponds to the

solid state structure of mirror symmetry in Fig. 1. The dou-blets centered at ds8.92 and 8.67 ppm in the intensity ratioof 1:2 are attributed to the ortho-protons on the pyridyl ringstrans and cis to the acetate group, respectively. This obser-vation indicates that the acetate group rotates freely along theRu–O2 bond, leading to the equivalence of both the cis pyr-idyl rings. The other protons on the pyridyl rings show signalsin the range 7.15–7.75 ppm which overlap with the signalsfrom the toluene molecules. The pyridylmethyl proton signalson the pyridyl rings trans and cis to the acetate appear at 5.37(s) and 5.20 (d) ppm, respectively, in the intensity ratio of1:2. The singlet at 1.78 ppm is assigned to the acetate protons.The methyl proton singlet from toluene appears at 1.26 ppm.

Supplementary material

Atomic coordinates, anisotropic thermal parameters andcomplete bond distances and bond angles of 1 have beendeposited at the Cambridge Crystallographic Data Center.Tables of structure factors and other structural details areavailable from the authors on request.

L. Xu, Y. Sasaki / Inorganic Chemistry Communications 2 (1999) 121–123 123

Tuesday Mar 30 11:26 AM StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications) Article: 164

Acknowledgements

The authors are grateful to the Japan Society for the Pro-motion of Science for a Fellowship to LX, and to Dr. KeisukeUmakoshi of Hokkaido University for valuable discussions.Grant-in-Aids No. 09554037 and No. 09237106 (PriorityArea of ‘Electrochemistry of Ordered Interface’) from theMinistry of Education, Science, Sports, and Culture, Japan,is also acknowledged

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