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) Complexesviaa Dilithio-Derivative. Crystal Structure of the Pd Dimer [ClPd{2,6-(Me2NCH2)2C6H2}]2

The potentially bis-cyclometalating ligand 3,3‘,5,5‘-tetrakis[(dimethylamino)methyl]biphenyl, was prepared from 3,5-(Me 2 NCH 2 ) 2 C 6 H 3 Br 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-(Me 2 NCH 2 ) 2 C 6 H 2 } 2 ] n, which is a versatile precursor to bimetallic complexes via a double transmetalation reaction. The syntheses and characterization of the new homobinuclear Pt(II) and Pd(II) compounds, [(MeCN)Pt{2,6-(Me 2 NCH 2 ) 2 C 6 H 2 }−] 2 (CF 3 SO 3 ) 2 and [ClPd{2,6-(Me 2 NCH 2 ) 2 C 6 H 2 }−] 2, is reported in addition to a novel synthetic route to the complex [ClPt{2,6-(Me 2 NCH 2 ) 2 C 6 H 2 }−] 2 . The solid-state structure of Pd dimer was determined by single-crystal X-ray diffraction. Oxidative addition of Cl 2 to the latter Pt compound produced the bis-platinum(IV) complex [Cl 3 Pt{2,6-(Me 2 NCH 2 ) 2 C 6 H 2 }−] 2, which reacts with 2 equiv of Ag(O 3 SCF 3 ) in MeCN solution to form [(MeCN)Cl 2 Pt{2,6-(Me 2 NCH 2 ) 2 C 6 H 2 }−] 2 (CF 3 SO 3 ) 2 . This complex could also be obtained directly by reaction of the former Pt II dimer with 2 equiv of Cl 2 IPh. 1 H NMR spectroscopic studies show that mixtures of the Pt II and Pt IV dimers in acetonitrile solution are in equilibrium with a mixed-valence (Pt II,Pt IV ) species [(MeCN)Pt II {2,6-(Me 2 NCH 2 ) 2 C 6 H 2 −C 6 H 2 (CH 2 NMe 2 )-2,6}Pt IV Cl 2 (NCMe)](CF 3 SO 3 ) 2, which, however, could not be isolated in pure form. The reaction of the Pt II dimer with ≤1 equiv of Cl 2 IPh also gave a Pt IV dimer, along with unreacted starting material and the mixed-valence complex. A reversible double C−C bond formation has been achieved by reaction of the Pt II dimer with excess of methyl iodide. This procedure yields the bis(arenonium) species [IPt II {2,6-(Me 2 NCH 2 ) 2 -1-MeC 6 H 2 }−] 2 (CF 3 SO 3 ) 2 in which both the Me groups derived from I−Me bond cleavage are bound to the C ipso of the aryl rings. The mono(arenonium) compound [IPt II {2,6-(Me 2 NCH 2 ) 2 -1-MeC 6 H 2 -C 6 H 2 (CH 2 NMe 2 ) 2 -2‘,6‘}Pt II ](CF 3 SO 3 ) 2 has been identified as an intermediate in this reaction by 1 H NMR spectroscopy.