Cyclohexyneplatinum(0) Complexes Containing Di-t-butylphenylphosphine, t-butyldiphenylphosphine or Trimethylphosphine

Abstract

Cyclohexyneplatinum (0) complexes Pt(C₆H₈)L₂ [L = PBu^t₂Ph(4), Pbu^tPh₂(5)] analogous to the known complex (3) (L=PPh₃) have been prepared by reaction of the two-coordinate complexes PtL₂ with 1,2-dibromocyclohexene and 1% sodium amalgam. The corresponding tricyclohexylphosphine complex is formed by a similar reaction but it could not be isolated in a pure state. Attempts to prepare analogues of (4) and (5) containing cycloheptyne or cyclooctyne were unsuccessful, possibly because the bulky t-butyl groups of the tertiary phosphines hinder coordination of the larger rings. Bulky tertiary phosphines do not displace PPh₃ from (3) but trimethylphosphine reacts with (3) to give successively Pt(C⁶H⁸)(PMe³)2(PPh³) (10) and Pt(C⁶H⁸)(PMe³)2 (11), as shown by ³¹P{¹H) n.m.r. spectroscopy. The tertiary phosphines in these complexes equilibrate rapidly at room temperature in benzene and only (10) can be isolated as a solid from the reaction. Complexes (4) and (5) react with HCl (1 molar proportion) to give n¹-cyclohexen-l-yl complexes trans- PtCl (C⁶H⁹)L² [L= PBu^t₂Ph(6), PBu^tPh₂ (7)]. In the absence of air, (4) reacts with methanol at 65°C to give the hydrido complex trans- PtH (C₆H₉)(PBu^t₂Ph)₂ (8). In the presence of oxygen from the air, however, the main product is the dioxygen complex Pt(O₂)(Pbu^t₂Ph)₂ (9). This represents an unusual example of complete displacement of cyclohexyne from a platinum(0) complex by a π-acceptor ligand.