Some chemistry of the heterobimetallic complexes [(OC)3Mo(µ-dppm)2Rh(CO)Cl] and [(OC)3Mo(µ-dppm)2M(CO)2]PF6(M = Rh or Ir, dppm = Ph2PCH2PPh2). Structure of [(OC)3Mo(µ-dppm)2(µ-CCMe)Rh(CO)]

Abstract

The previously described complex [(OC)₃Mo(µ-dppm)₂Rh(CO)Cl](Ia) does not readily undergo metathesis, thus when treated with NaI it gave [(OC)₃Mo(µ-dppm)₂Rh(CO)I] in only ca. 50% yield even after 3 h. However, the salt [(OC)₃Mo(µ-dppm)₂Rh(CO)₂]PF₆(2a) when treated with NH₄Br, NH₄I, NaN₃, or NaCN gave complexes of type [(OC)₃Mo(µ-dppm)₂Rh(CO)X](X = Br, I, N₃, or CN) in good yield. ³¹P-{¹H} N.m.r. evidence suggests that [(OC)₃Mo(µ-dppm)₂Rh(CO)Br] occurs in two forms, a major form analogous to (1a) and a minor form (3) which possibly has a semibridging CO. Complex (1a) or (2a) reacts with NaBH₄ to give a hydrido complex [(OC)₃Mo(µ-dppm)₂Rh(CO)H]. Treatment of (2a) with Li(CCR) gave the acetylide complexes [(OC)₃Mo(µ-dppm)₂(µ-CCR)Rh(CO)](R = Me, Ph, or C₆H₄Me-p)(4a)–(4c). Treatment of (1a) or (2a) with MeCN in the presence of PF₆^– gave the complex [(OC)₃Mo(µ-dppm)₂Rh(CO)(NCMe)]PF₆. The previously described [(OC)₃Mo(µ-dppm)₂Ir(CO)₂]PF₆ reacts similarly with NCR (R = Me or Ph) to give the analogous nitrile complexes [(OC)₃Mo(µ-dppm)₂Ir(CO)(NCR)]PF₆. Treatment of (1a) or (2a) with Bu^tNC gives [(OC)₃Mo(µ-dppm)₂Rh(CO)(CNBu^t)]⁺. Crystals of the compound [(OC)₃Mo(µ-dppm)₂(µ-CCMe)Rh(CO)] are triclinic, space group P, with a= 1 802.2(3), b= 1 303.2(3), c= 1 228.2(3) pm, α= 114.77(2), β= 97.52(2), γ= 102.02(2)°, and Z= 2; final R′ factor 0.037 for 6 006 observed reflections. The structure shows that the two metal centres [Mo ⋯ Rh 312.2(0) pm] are asymmetrically bridged by methylacetylide which forms a σ bond to rhodium and a side-on π bond to molybdenum.