SYNTHESIS AND CHARACTERIZATION OF THE BIS-CYCLOMETALATING LIGAND 3,3',5,5'-TETRAKIS[(DIMETHYLAMINO)METHYL]BIPHENYL AND ITS USE IN THE PREPARATION OF BIMETALLIC M(II), M(IV) (M = PT, PD), AND MIXED-VALENCE PT(II)-PT(IV) COMPLEXES VIA A DILITHIO-DERIVATIVE - CRYSTAL-STRUCTURE OF THE PD DIMER [CLPD(2,6-(ME2NCH2)(2)C6H2)](2)

The potentially bis-cyclometalating ligand 3,3',5,5'-tetrakis[(dimethy lamino)methyl biphenyl, was prepared from 3,5-(Me2NCH2)(2)C6H3Br in a one-pot synthesis involving lithium-halogen exchange, transmetalation, and reductive-elimination reactions. This ligand undergoes selective dilithiation in the 4 and 4' positions of the biphenyl group to form [ Li-2{2,6-(Me2NCH2)(2)C6H2}(2)](n), which is a versatile precursor to b imetallic complexes via a double transmetalation reaction. The synthes es and characterization of the new homobinuclear Pt(II) and Pd(II) com pounds, [(MeCN)Pt{2,6-(Me2NCH2)(2)C6H2}-](2)(CF3SO3)(2) and [ClPt{2,6- (Me2NCH2)(2)C6H2}-](2), is reported in addition to a novel synthetic r oute to the complex [ClPt{2,6-(Me2NCH2)(2)C6H2}-](2). The solid-state structure of Pd dimer was determined by single-crystal X-ray diffracti on. Oxidative addition of Cl-2 to the latter Pt compound produced the bis-platinum(IV) complex [Cl3Pt{2,6-(Me2NCH2)(2)C6H2)-](2), which reac ts with 2 equiv of Ag(O3SCF3) in MeCN solution to form (MeCN)Cl2Pt{2,6 -(Me2NCH2)(2)C6H2}-](2)(CF3SO3)(2). This complex could also be obtaine d directly by reaction of the former Pt-II dimer with 2 equiv of Cl2IP h. H-1 NMR spectroscopic studies show that mixtures of the Pt-II and P t-IV dimers in acetonitrile solution are in equilibrium with a mixed-v alence (Pt-II,Pt-IV) species C6H2(CH2NMe2)-2,6}(PtCl2)-Cl-IV(NCMe)](CF 3SO3)(2), which, however, could not be isolated in pure form. The reac tion of the Pt-II dimer with less than or equal to 1 equiv of Cl2IPh a lso gave a Pt-IV dimer, along with unreacted starting material and the mixed-valence complex. A reversible double C-C bond formation:has bee n achieved by reaction of the Pt-II dimer with excess of methyl iodide . This procedure yields the bis(arenonium) species [IPtII{2,6-(Me2NCH2 )(2)-1-MeC6H2}-](2)(CF3SO3)(2) in which both the Me groups derived fro m I-Me bond cleavage are bound to the C-ipso of the aryl rings. The mo no-(arenonium) compound -1-MeC6H2-C6H2(CH2NMe2)(2)-2',6'}Pt-II](CF3SO3 )(2) has been identified as an intermediate in this reaction by 1H NMR spectroscopy.