Nucleophilic (Michael) additions to (Ph2P)2CCH2 when chelated to platinum(II) dichloride or di-iodide

Abstract

Treatment of [PtCl₂(NCBu^t)₂] with (Ph₂P)₂CCH₂(vdpp) in dichloromethane gave [PtCl₂(vdpp-PP′)](1a). Treatment of (1a) with a variety of amines or NN-dimethylhydrazine in dichloromethane gave the Michael addition products rapidly and in good yields, viz. [PtCl₂{(Ph₂P)₂- CHCH₂NHR}][R = NMe₂(2a), CH₂CHCH₂(3), D-CHMePh (4), or CH₂C₆H₄OMe-4 (5a)]. Complex (1a) is more reactive towards Michael addition than is [PtMe₂(vdpp-PP′)]; thus it forms adducts with H₂NC₆H₄Me-4 or H₂NCH₂CO₂Et, i.e. [PtCl₂{(Ph₂P)₆CHCH₂NHC₆H₄Me-4}](7) or [PtCl₂{(Ph₂P)₂CHCH₂NHCH₂CO₂Et}](8). It is also remarkably reactive towards carbon nucleophiles, e.g. with 1 equivalent of ethyl acetoacetate or acetylacetone in dichloromethane in the presence of anhydrous sodium carbonate it gave [PtCl₂{(Ph₂P)₂CHCH₂CH(COMe)(CO₂Et)}](10) or [PtCl₂{(Ph₂P)₂CHCH₂CH(COMe)₂}](11), respectively. On prolonged treatment of (1a) with sodium iodide in acetone, acetone added to the vinylidene double bond to give [PtI₂{(Ph₂P)₂CHCH₂CH₂COMe}](13a). The di-iodo-complex [PtI₂(vdpp-PP′)](1b) was prepared by treating (1a) with NBuⁿ₄I in dichloromethane. Complex (1b) reacted with Me₂NNH₂ or amine to give adducts, e.g. [PtI₂{(Ph₂P)₂CHCH₂NHNMe₂}](2b) or [PtI₂{(Ph₂P)₂-CHCH₂ NHCH₂C₆H₄OMe-4}](5b), but not with carbon nucleophiles under conditions when the corresponding dichloro-complex (1a) underwent Michael addition. Variable-temperature n.m.r. spectroscopy was used to compare the rates of some of these reactions; ³¹P-{¹H}, ¹H-(³¹P), and ¹H n.m.r. and i.r. data are given.