title: Investigation of the stability of the M-H-B bond in borane sigma complexes [M(CO)5(eta1-BH2R.L)] and [CpMn(CO)2(eta1-BH2R.L)] (M=Cr, W; L=tertiary amine or phosphine): substituent and Lewis base effects.
abstract: We investigated the influence of a substituent and a Lewis base on boron upon the thermodynamic stability of metal complexes of borane-Lewis base adducts, [M(CO)5(eta1-BH(2)R.L)] (M=Cr, W) and [CpMn(CO)2(eta1-BH2R.L)], where R=Cl, I, m-C6H4F, Ph, H, Me, Et; L=PMe3, PPh3, NMe3, quinuclidine. In these compounds, the stability of the metal-borane linkage was enhanced by increasing the electron-releasing ability of the substituent on boron. A stronger base L additionally stabilized the complexes. The strength of the borane-metal interaction is thus mainly ascribed to the electron donation from the BH sigma orbital to metal rather than the back-donation into the BH sigma* orbital. This result supports the bonding model for the B-H-M linkage in the borane complexes suggested by MO calculations, where the borane-to-metal electron donation is predominant while the metal back-donation into the BH sigma* orbital is negligible. Such a stability trend of the borane complexes makes a sharp contrast to that of many silane and dihydrogen complexes.
authors.affiliation: Department of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan. ckawano1@mail.ecc.u-tokyo.ac.jp
authors.forename: Yasuro
authors.initials: Y
authors.lastname: Kawano
authors.forename: Kazunori
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Shun-ya
authors.initials: SY
authors.lastname: Miyake
authors.forename: Taeko
authors.initials: T
authors.lastname: Kakizawa
authors.forename: Mamoru
authors.initials: M
authors.lastname: Shimoi
mesh_terms: D000588:Amines / Q000737:chemistry*; D001880:Boranes / Q000138:chemical synthesis / Q000737:chemistry*; D001895:Boron / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry*; D017608:Chromium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D017895:Manganese Compounds / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D010720:Phosphines / Q000737:chemistry*; D011522:Protons; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000588:Amines; D001880:Boranes; D017608:Chromium Compounds; D017895:Manganese Compounds; D010720:Phosphines; D011522:Protons; D002248:Carbon Monoxide; D006859:Hydrogen; C044646:phosphine; D001895:Boron