Properties of the [M(dppm)2M']2+ Building Blocks (M, M' = Pd or Pt): Site Selectivity, Emission Features, and Frontier Orbital Analysis.

The homodinuclear [CIM(μ-dppm)2MCI] complexes 1 (M = Pd) and 2 (M = Pt) react with RNC ligands (R = Ph, xylyl, p-tolyl, p-C6H4iPr) to provide the A-frame [CIPd(μ-dppm)2(μ-C=N-R)PdCI] (R = Ph (5a), xylyl (5b)), [CIPt(μ-dppm)2(μ-C=N-R)PtCI] (R = p-tolyl (4a); p-C6H4iPr (4b)), and the d9-d9 M2-bonded [CIPt(μ-dppm)2Pt(CN-R)]Cl (R = xylyl (3a); p-C6H4iPr (3b)) complexes. The heterodinuclear [XPd(μ-dppm)2PtX] complexes 6a (X = Cl) and 6b (X = I) react with RNC (R = o-anisyl) to form the A-frame [XPd(μ-dppm)2(μ-C=N-R)PtX] (X = Cl (9); I (10a)) and M2-bonded [CIPt(μ-dppm)2Pt(CN-R)]Cl (10b) complexes. The dangling ligand-containing complex [CIPd(u- dppm)2Pt(η1-dppm=O)](BF4) (7) reacts with xylyl-NC stoichiometrically to produce the dicationic salt [(xylyl-NC)Pd(μ-dppm)2Pt(η1-dppm=O)](BF4)2 (8). Parameters ruling the coordination site terminal versus bridging are discussed. The precursor 10a reacts with RNC (R = o-anisyl, tBu) to form the heterobimetallic bis(isonitrile) [lPd(μ-dppm)2(μ-C=N-o-anisyl)Pt(CN-R)]l complexes 11b and 12, respectively, demonstrating the site selectivity of the second CNR ligand coordination, Pd versus Pt. The X-ray structures of 11b and 12 were obtained. Complex 12 is the first example of an A-frame system of the Ni-triad bearing two different isocyanide ligands. Several d9-d9 terminal and d8-d8 A-frame homo- and heterodinuclear complexes in 2-MeTHF at 77 K were studied by UV-vis and luminescence spectroscopy. Assignments for the lowest energy absorption and emission bands are made on the basis of density functional theory and time-dependent density functional theory computations. [ABSTRACT FROM AUTHOR]