UNUSUALLY STABLE 4-MEMBERED CHELATE RINGS IN NICKEL(II), PALLADIUM(II), AND PLATINUM(II) COMPLEXES WITH THE LIGAND 2,2-BIS(DIPHENYLPHOSPHINO)PROPANE (2,2-DPPP) - CRYSTAL AND MOLECULAR-STRUCTURE OF [PDI2(2,2-DPPP)]CENTER-DOT-0.8CH(2)CL(2)

The ligand Ph2PC(CH3)(2)PPh2 (2,2-dppp) reacts with Ni(II) salts to gi ve robust square-planar chelate complexes [NiX2(2,2-dppp-P,P')] (X = C l, 1; X = Br, 2) and the salt [Ni(2,2-dppp)(2)](ClO4)(2) (3). The Pd(I I) analogues [PdCl2(2,2-dppp)] (4), [PdI2(2,2-dppp)] (5), and [Pd(2,2- dppp)(2)](BF4)(2) (6) have also been made. The crystal structure of 5 (obtained as 5.0.8CH(2)Cl(2)) has been determined by X-ray diffraction . The geminal C(CH3)(2) group, when compared with related Ph2PCH2PPh2 (dppm) complexes, causes a small compression of the P-C-P chelate ring angle (to 91.3(3)degrees for 5). With [PtCl2(PhCN)(2)], 2,2-dppp affo rds [PtCl2-(2,2-dppp)] (7), which undergoes metathesis with NaI to giv e [PtI2(2,2-dppp)] (8), and [Pt(2,2-dppp)(2)]Cl-2 (9) was obtained by reaction of [PtCl2(PhCN)(2)] with 2 equiv of 2,2-dppp. Reactions were then attempted with 7 and 9, which are known to result in ring-opening reactions with the corresponding complexes of dppm, but in all cases, only 2,2-dppp chelate complexes could be isolated. Thus, treatment of 7 or 9 with excess MeLi gave exclusively [PtMe2(2,2-dppp)] (10) rathe r than cis,cis-[Pt2Me4(2,2-dppp)(2)]. Attempts to ring-open 10 with ex cess 2,2-dppp to give cis-[PtMe2(2,2-dppp-P)(2)] were unsuccessful. Tr eatment of 10 with 1 equiv of HCl or, better, treatment of [PtCl(Me)(1 ,5-cyclooctadiene)] with 2,2-dppp gave only mononuclear [PtCl(Me)(2,2- dppp)] (11) and no dimer of the type [MePt(mu-2,2-dppp)(2)(mu-Cl)PtMe] Cl. Treatment of 7 with 2 equiv of NaCN in EtOH gave the chelate compl ex [Pt(CN)2(2,2-dppp)] (12) rather than trans, trans-[Pt-2(CN)(4)(mu-2 ,2-dppp)(2)], and treatment of 7 with LiC=CPh in thf or (better) H2NNH 2 . H2O/HC=CPh in EtOH gave [Pt(C=CPh)(2)(2,2-dppp)] (13), rather than trans,trans-[Pt-2(C=CPh)(4)(mu-2,2-dppp)(2)]. Reaction of 7 with LiC= CBun in thf likewise gave [Pt(C=CBun)(2)(2,2-dppp)] (14) in low yield. The complexes were characterized by microanalyses (C, H, N and, in so me cases, halide), infrared spectroscopy, (31)p{H-1} and H-1 NMR spect roscopy, and fast atom bombardment mass spectrometry.