Platinum(II) hydride silanone complexes and cyclic trimers of silanone. A theoretical study of their geometries, bonding nature, and stabilities

Platinum(II) hydride silanone complexes [PtH(dipe)(R2SiO)](+) (R = H, F, CH 3, CF3, or SiH3; dipe = H2PCH2CH2PH2), their acetone and ethylene analogues , and cylic trimers of silanone, (R2SiO)(3), were theoretically investigate d with the DFT method. Unexpectedly, the platinum(II) hydride silanone comp lex does not involve a usual eta (2)-SiO coordinate bond with the platinum center but two bonding interactions, one between the O atom and the platinu m center and the other between the Si atom and the hydride ligand. The form er interaction mainly consists of electron donation from a silanone pi orbi tal to a Pt d orbital, while the latter one consists of back-donation from the hydride 1s orbital to the silanone pi* orbital, as well as the electros tatic stabilization interaction between the Si atom and the hydride ligand. In the acetone analogue, on the other hand, only the O atom interacts with the platinum center, but the C atom does not interact with any part of [Pt H(dipe)](+). The Si=O bond lengthens by about 0.1 Angstrom and the SiR2 pla ne is bent back away from the platinum center by 20-30 degrees, while the C =O and C=C bonds lengthen upon coordination of acetone and ethylene to a mu ch lesser extent than does the Si O bond. The binding energy of silanone wi th the platinum(II) hydride complex is much larger than those of ethylene a nd acetone, because the former complex involves an additional Si-H bonding interaction. The binding energy of the platinum(II) hydride silanone comple x increases as the silanone pi orbital rises in energy, which indicates tha t the donating interaction participates in the coordinate bond to a greater extent than does the back-donating interaction. Cyclic trimers of silanone are planar, in which the Si atom takes sp(3) hybridization. The silanone t rimers are formed from silanone monomers with significantly large stabiliza tion energy of 60-80 kcal/mol per molecule of silanone. Despite the conside rably large binding energy of the platinum(II) hydride silanone complex, it easily converts to the di(mu -hydride)diplatinum(II) complex, [Pt(mu -H)(d ipe)](2)(2+) with formation of a cyclic trimer of silanone because of the s ignificantly large stabilization energies of silanone trimer and [Pt(mu -H) (dipe)](2)(2+). Hence, the platinum(II) hydride complex is not useful to is olate the transition-metal silanone adduct. Molybdenum(0) and zirconium(II) complexes, Mo(dipe)(2)(R2SiO)(2) (R = H or CH3) and Cp2Zr(Me2SiO), were al so theoretically investigated. These complexes involve the usual eta (2)-Si O coordinate bond expectedly, in which the pi -back-donating interaction is much stronger than the sigma -donating interaction. Though the binding ene rgy of silanone with Mo(dipe)(2) is as large as that with [PtH(dipe)](+), c oordination of silanone with Cp2Zr yields a significantly large binding ene rgy of about 90 kcal/mol. We wish to propose that Cp2Zr is one of the usefu l complexes to isolate a transition-metal silanone adduct.