Properties of Borane, the BH Molecule - MITweb.mit.edu/5.03/www/readings/electron_deficient/... ·...

Properties of Borane, the BH3 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Diborane, B2H6, is a colorless gas forming explosive mixtureswith air

Diborane is endothermic with ∆H◦f = 36 kJ/mol

Despite this thermodynamic stability, diborane is kineticallynot so reactive but takes place in many reactions involvingloss of H2

Industrial synthesis: 8 BF3 + 6 LiH −→ B2H6 + 6 LiBF4

Convenient laboratory synthesis: 2 NaBH4 + I2 −→ 2 NaI +B2H6 + H2

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Diborane, B2H6, is a colorless gas forming explosive mixtureswith air

Diborane is endothermic with ∆H◦f = 36 kJ/mol

Despite this thermodynamic stability, diborane is kineticallynot so reactive but takes place in many reactions involvingloss of H2

Industrial synthesis: 8 BF3 + 6 LiH −→ B2H6 + 6 LiBF4

Convenient laboratory synthesis: 2 NaBH4 + I2 −→ 2 NaI +B2H6 + H2

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Diborane, B2H6, is a colorless gas forming explosive mixtureswith air

Diborane is endothermic with ∆H◦f = 36 kJ/mol

Despite this thermodynamic stability, diborane is kineticallynot so reactive but takes place in many reactions involvingloss of H2

Industrial synthesis: 8 BF3 + 6 LiH −→ B2H6 + 6 LiBF4

Convenient laboratory synthesis: 2 NaBH4 + I2 −→ 2 NaI +B2H6 + H2

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Diborane, B2H6, is a colorless gas forming explosive mixtureswith air

Diborane is endothermic with ∆H◦f = 36 kJ/mol

Despite this thermodynamic stability, diborane is kineticallynot so reactive but takes place in many reactions involvingloss of H2

Industrial synthesis: 8 BF3 + 6 LiH −→ B2H6 + 6 LiBF4

Convenient laboratory synthesis: 2 NaBH4 + I2 −→ 2 NaI +B2H6 + H2

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Diborane, B2H6, is a colorless gas forming explosive mixtureswith air

Diborane is endothermic with ∆H◦f = 36 kJ/mol

Despite this thermodynamic stability, diborane is kineticallynot so reactive but takes place in many reactions involvingloss of H2

Industrial synthesis: 8 BF3 + 6 LiH −→ B2H6 + 6 LiBF4

Convenient laboratory synthesis: 2 NaBH4 + I2 −→ 2 NaI +B2H6 + H2

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Alfred Stock pioneered the chemistry of the boron hydridesusing vacuum-line techniques

Stock proposed an ethane-like structure for diborane

S. H. Bauer in 1937 reported electron diffractionmeasurements interpreted (DOI: 10.1021/ja01285a041) insupport of the ethane-like structure

The ethane-like structure required resonance structures withone-electron bonds

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Alfred Stock pioneered the chemistry of the boron hydridesusing vacuum-line techniques

Stock proposed an ethane-like structure for diborane

S. H. Bauer in 1937 reported electron diffractionmeasurements interpreted (DOI: 10.1021/ja01285a041) insupport of the ethane-like structure

The ethane-like structure required resonance structures withone-electron bonds

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Alfred Stock pioneered the chemistry of the boron hydridesusing vacuum-line techniques

Stock proposed an ethane-like structure for diborane

S. H. Bauer in 1937 reported electron diffractionmeasurements interpreted (DOI: 10.1021/ja01285a041) insupport of the ethane-like structure

The ethane-like structure required resonance structures withone-electron bonds

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

Alfred Stock pioneered the chemistry of the boron hydridesusing vacuum-line techniques

Stock proposed an ethane-like structure for diborane

S. H. Bauer in 1937 reported electron diffractionmeasurements interpreted (DOI: 10.1021/ja01285a041) insupport of the ethane-like structure

The ethane-like structure required resonance structures withone-electron bonds

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

1943 (DOI: 10.1039/JR9430000250) undergraduate studentH. C. Longuet-Higgins (Balliol College, Oxford) and R. P. Bellproposed B-H-B bridge bonds instead with a D2h symmetrystructure

In 1941 a U. of Chicago chemistry professor Schlesingerworking on the Manhattan project wrote a letter to LinusPauling suggesting the same structure with B-H-B bridgebonds (A Diborane Story, Pierre Laszlo, ACIE 2000, 39,2071); Pauling responded unfavorably

Mulliken weighed in (1947) with an MO analysis favoring theD2h structure because of agreement with electronic absorptionspectra

Price interpreted the IR data in terms of the D2h structureand gave assignments

Shoolery reported clinching NMR data in 1955

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

1943 (DOI: 10.1039/JR9430000250) undergraduate studentH. C. Longuet-Higgins (Balliol College, Oxford) and R. P. Bellproposed B-H-B bridge bonds instead with a D2h symmetrystructure

In 1941 a U. of Chicago chemistry professor Schlesingerworking on the Manhattan project wrote a letter to LinusPauling suggesting the same structure with B-H-B bridgebonds (A Diborane Story, Pierre Laszlo, ACIE 2000, 39,2071); Pauling responded unfavorably

Mulliken weighed in (1947) with an MO analysis favoring theD2h structure because of agreement with electronic absorptionspectra

Price interpreted the IR data in terms of the D2h structureand gave assignments

Shoolery reported clinching NMR data in 1955

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

1943 (DOI: 10.1039/JR9430000250) undergraduate studentH. C. Longuet-Higgins (Balliol College, Oxford) and R. P. Bellproposed B-H-B bridge bonds instead with a D2h symmetrystructure

In 1941 a U. of Chicago chemistry professor Schlesingerworking on the Manhattan project wrote a letter to LinusPauling suggesting the same structure with B-H-B bridgebonds (A Diborane Story, Pierre Laszlo, ACIE 2000, 39,2071); Pauling responded unfavorably

Mulliken weighed in (1947) with an MO analysis favoring theD2h structure because of agreement with electronic absorptionspectra

Price interpreted the IR data in terms of the D2h structureand gave assignments

Shoolery reported clinching NMR data in 1955

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

1943 (DOI: 10.1039/JR9430000250) undergraduate studentH. C. Longuet-Higgins (Balliol College, Oxford) and R. P. Bellproposed B-H-B bridge bonds instead with a D2h symmetrystructure

In 1941 a U. of Chicago chemistry professor Schlesingerworking on the Manhattan project wrote a letter to LinusPauling suggesting the same structure with B-H-B bridgebonds (A Diborane Story, Pierre Laszlo, ACIE 2000, 39,2071); Pauling responded unfavorably

Mulliken weighed in (1947) with an MO analysis favoring theD2h structure because of agreement with electronic absorptionspectra

Price interpreted the IR data in terms of the D2h structureand gave assignments

Shoolery reported clinching NMR data in 1955

5.03 Inorganic Chemistry

Borane Exists as a Dimer: Diborane

1943 (DOI: 10.1039/JR9430000250) undergraduate studentH. C. Longuet-Higgins (Balliol College, Oxford) and R. P. Bellproposed B-H-B bridge bonds instead with a D2h symmetrystructure

In 1941 a U. of Chicago chemistry professor Schlesingerworking on the Manhattan project wrote a letter to LinusPauling suggesting the same structure with B-H-B bridgebonds (A Diborane Story, Pierre Laszlo, ACIE 2000, 39,2071); Pauling responded unfavorably

Mulliken weighed in (1947) with an MO analysis favoring theD2h structure because of agreement with electronic absorptionspectra

Price interpreted the IR data in terms of the D2h structureand gave assignments

Shoolery reported clinching NMR data in 1955

5.03 Inorganic Chemistry

Structure for the B2H6 MoleculeGraphic from Price, 1948, DOI: 10.1063/1.1747028

5.03 Inorganic Chemistry

Structure for the B2H6 MoleculeA different way of writing the bridge bonds

H BH HB H

H

H

5.03 Inorganic Chemistry

Borohydride Ion [BH4]− has Td Symmetry

-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.53.03.54.01H NMR (ppm)

-0.8

1-0

.71

-0.6

4-0

.61

-0.5

7-0

.50

-0.4

4-0

.41

-0.3

7-0

.30

-0.2

0

1.93

1.94

1.95

1.95

CD3CN

NaBH4

5.03 Inorganic Chemistry

MO Calculations on the B2H6 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

This is one of the four terminal 2c-2e B-H bonds

5.03 Inorganic Chemistry

MO Calculations on the B2H6 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

This is one of the four terminal 2c-2e B-H bonds

5.03 Inorganic Chemistry

MO Calculations on the B2H6 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

This is one of the two 3c-2e B-H bridge bonds

5.03 Inorganic Chemistry

MO Calculations on the B2H6 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

This is one of the two 3c-2e B-H bridge bonds

5.03 Inorganic Chemistry

Resonance Structures for the B2H6 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation

5.03 Inorganic Chemistry

Reaction of Borane THF Adduct with CO2Mizuta et al. Organometallics, 2014, 33, pp 6692–6695 DOI: 10.1021/om5008488

The reaction between commercially available borane solutionsand CO2 had not been reported!

The product of this reaction is called trimethoxyboroxine, withCO2 reduced to the level of methanol

5.03 Inorganic Chemistry

Reaction of Borane THF Adduct with CO2Mizuta et al. Organometallics, 2014, 33, pp 6692–6695 DOI: 10.1021/om5008488

The reaction between commercially available borane solutionsand CO2 had not been reported!

The product of this reaction is called trimethoxyboroxine, withCO2 reduced to the level of methanol

5.03 Inorganic Chemistry

Reaction of Borane THF Adduct with CO2Mizuta et al. Organometallics, 2014, 33, pp 6692–6695 DOI: 10.1021/om5008488

The reaction between commercially available borane solutionsand CO2 had not been reported!

The product of this reaction is called trimethoxyboroxine, withCO2 reduced to the level of methanol

5.03 Inorganic Chemistry

Donor-Acceptor BondsTypically written with an arrow or with a line and formal charges

A donor-acceptor bond can be written this way: Me2O:→BH3

Alternatively it can be written this way: Me2O+–B−H3

A donor-acceptor complex forms with a Lewis base donatingan electron pair to a Lewis acid

5.03 Inorganic Chemistry

Donor-Acceptor BondsTypically written with an arrow or with a line and formal charges

A donor-acceptor bond can be written this way: Me2O:→BH3

Alternatively it can be written this way: Me2O+–B−H3

A donor-acceptor complex forms with a Lewis base donatingan electron pair to a Lewis acid

5.03 Inorganic Chemistry

Donor-Acceptor BondsTypically written with an arrow or with a line and formal charges

A donor-acceptor bond can be written this way: Me2O:→BH3

Alternatively it can be written this way: Me2O+–B−H3

A donor-acceptor complex forms with a Lewis base donatingan electron pair to a Lewis acid

5.03 Inorganic Chemistry

Donor-Acceptor BondsTypically written with an arrow or with a line and formal charges

A donor-acceptor bond can be written this way: Me2O:→BH3

Alternatively it can be written this way: Me2O+–B−H3

A donor-acceptor complex forms with a Lewis base donatingan electron pair to a Lewis acid

5.03 Inorganic Chemistry