Cationic Pt(IV) Tp' carbenes

Abstract A series of Pt(IV) carbene complexes of the form [(Tp')Pt(=C(X)(Y))(Me) 2 ] + (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate) was synthesized. Methylating a series of Pt-carboxamido precursors allowed isolation of [(Tp')Pt(=C(OMe)NHR)Me 2 ][OTf] (R = Et, n Pr, i Pr, Bn). The solid-state structures of the Pt-carbene complexes reveal resonance-stabilized cationic carbene complexes. The method for generating these rare Pt(IV) carbenes was extended to synthesize a methoxy stabilized Pt carbene complex, [Tp'Pt(=C(OCH 3 )CH 3 )Me 2 ][OTf], from a Pt-acyl precursor. Preparation of an alkylidene analog proved more challenging, but low temperature protonation (−80 °C) of a Pt-vinyl complex, (Tp')Pt(CH CH 2 )(Me) 2 , generated a small amount of an ethylidene Pt complex as monitored by NMR. Low temperature NMR indicated the presence of the Pt CH(CH 3 ) unit in [(Tp')Pt(=CH(CH 3 )Me 2 ][B(Ar F ) 4 ]. The 13 C labeling studies revealed the carbene carbon signal at 500 ppm, a dramatic downfield chemical shift. Warming the reaction to −40 °C results in isomerization accompanied by protonation of a Tp' nitrogen and reductive elimination to form a new C–C bond in a Pt(II) propylene adduct, [κ 2 (Tp' (NH) )Pt(η 2 CH 2 CHCH 3 )Me][B(Ar F ) 4 ].