Modulation of an Anagostic Interaction in SiPSi-Type Pincer Platinum Complexes

The reactivities
of tris­(benzyldimethylsilyl)­phosphine [P­(o-C6H4-CH2SiMe2H)3] (1) and tris­(benzyldiphenylsilyl)­phosphine
[P­(o-C6H4-CH2SiPh2H)3] (6) toward the same platinum
precursor [Pt­(PPh3)3] are strikingly different.
The reaction with 1 renders the trans disilyl platinum­(II) complex [Pt­{P­(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}­PPh3] (2) in which the ligand coordinates in a tridentate
fashion while a new Si–C bond is formed from the third Si moiety.
The most prominent feature is an anagostic interaction that is established
at the apical position. In contrast, the reaction of [Pt­(PPh3)3] with 6 yields the hexacoordinated hydrido
trisilyl platinum­(IV) complex [PtH­{P­(o-C6H4-CH2SiPh2)3}­PPh3] (7). We have studied the effect of the variation
of the monodentate ligand in 2 by simple substitution
reactions. We found a systematic variation of the chemical shift of
the anagostic hydrogen in the 1H nuclear magnetic resonance
spectrum of the corresponding PMe3, P­(OPh)3,
and CO complexes that can in principle be ascribed to a varying degree
of the π acceptor character of the ancillary ligand. However,
theoretical calculations at the density functional theory level show
only slight changes in the frontier orbitals in line with predominantly
closed-shell electrostatic interactions.