Evidence for multiple bonding in four-coordinate, cationic, platinumthiosilylenes via AIM and CDA; effects of phosphine choice

Hybrid DFT/HF calculations were performed on five complexes (PH3)2(H)PtSi(SH)2+, (PH3)2(H)PtSi(SMe)2+, (PMe3)2(H)PtSi(SMe)2+, (PiPr3)2(H)PtSi(SEt)2+, and (PCy3)2(H)PtSi(SEt)2+, and analyzed using CDA and Atoms-In-Molecules. Complexes were found to possess both SiS and SiPt multiple bond character, in contrast to earlier results at lower levels of theory. The origins of twisted geometries were determined to be primarily steric in nature. Increasing the size of aliphatic substituents on the phosphines leads to a more balanced bonding motif, but increases steric repulsion, while changing the substituent at silicon from hydrogen to methyl resulted in a lengthening of the SiPt bond. Based on these results, the use of PH3 to substitute for PMe3 and larger groups in calculations is discouraged, though methyl is an acceptable, if not electronically identical, substitute for larger aliphatic phosphines.