Phosphorus-31 nuclear magnetic resonance studies of phosphido-bridged dinuclear complexes of palladium and platinum

Abstract

Proton decoupled 31P nmr spectra are reported for a series of dinuclear metal complexes containing bridging dialkyl- or diarylphosphido groups: [M2Cl2(μ-PR′2)2(PR3)2], M = Pd, R′ = Ph, R3 = Et3 or HPh2; M = Pd, R′ = Me, R3 = Et3, Ph3, or HMe2; M = Pt, R′ = Ph, R3 = Et3 or HPh2; and [M2(μ-PPh2)2(dppe)2]Cl2, M = Pd, or Pt, dppe = Ph2P(CH2)2PPh2. Detailed analysis and computer simulation of the spectra in the AA′XX′, AA′XX′M, AA′A″A′′′XX′, and AA′A′′A′′′XX′M spin systems leads to the following ranges and relative signs for coupling constants involving the bridging phosphorus atoms: 2J(R3P—cis PR′2), M = Pt, −1 to +5 Hz, M = Pd, +20 to +32 Hz; 2J(R3P—transPR′2), M = Pt, +291 to +396 Hz, M = Pd, +311 to +443 Hz; 2J(R2P—cis PR2), M = Pt, −162 to −208 Hz, M = Pd, −261 to −350 Hz (the assignment of negative signs to these couplings is not completely certain); 1J(Pt—PR2), trans to Cl, +2364 to +2635 Hz, trans to PR3, +1690 to +1992 Hz. Resonances due to the bridging phosphido groups occur at very high field (−267 to −322 ppm upfield of P(OCH3)3), in strong contrast to literature reports of phosphido bridges in palladium cluster complexes where the bridged metal atoms are linked by a metal–metal bond and the bridging phosphorus occurs +57 to +82 ppm downfield of P(OCH3)3.