Electronic Structure and Bonding in Hexacoordinate Silyl–Palladium Complexes Support from the National Science Foundation (CHE-9876792) is gratefully acknowledged.

Abstract

Trimerization of [Pd(R2PCH2CH2PR2){1,2-C6H4(SiH2)2}] (1; where R Me or Et) has been demonstrated to produce a trinuclear complex 2where two of the Pd atoms can be readily characterized as PdII centers but the nature of the third, central Pd atom is less clear (Scheme 1, by-products not shown).[1] While this Pd atom (Pd1) is drawn in Scheme 1 as bonding directly to two Si atoms and further interacting with two Si Si bonds, the interatomic distances from the X-ray crystal-structure data could also be interpreted to be consistent with an absence of Si Si bonds and instead six Pd Si bonds,[1] that is, the central metal would formally be PdVI. Both structures are without precedent in palladium coordination chemistry,[2, 3] although compounds of Pd[4±7] and Pt[8, 9] have been reported for inorganic compounds of the form [MFn] (M Pd, Pt; n 2,4,6), where the extreme electronegativity of fluorine is exploited for the generation of higher oxidation states.[10] To better understand the nature of the bonding in 2, we have carried out DFT calculations on 2 and relevant model compounds. With the exception of single-point calculations using the X-ray geometries of 2a and 2b, all the structures were fully optimized and verified as minima by analytic frequency calculations. The functional employed was of the hybrid variety[11] and combined exact Hartree ± Fock exchange with the gradient-corrected exchange and correlation functionals of Becke[12] and Lee, Yang, and Parr,[13] respecRu Ru