Organo–platinum–iron complexes derived from allenes. Crystal structures of [(OC)3Fe(µ-dppm){µ-C(O)CH2C(CH2)}Pt(PPh3)], [(OC)3Fe(µ-dppm)-{µ-C(CH2)CH2}Pt(PPh3)], and [(OC)2Fe(µ-dppm){η4-(CH2)(CMe2)CPt(PPh3)}

Abstract

Treatment of [(OC)3Fe(µ-dppm)(µ-CO)Pt(PPh3)](1)(dppm = Ph2PCH2PPh2) with allene at 20 °C in dichloromethane gave [(OC)3Fe(µ-dppm){µ-C(O)CH2C(CH2)}Pt(PPh3)](3) in moderate yield. Its structure was established by X-ray crystallography; the crystals are orthorhombic, space group Pbca with a= 2 481.5(3), b= 1 906.2(2), c= 1 838.7(3) pm, and Z= 8; R 0.0315 for 4 401 observed reflections. The allene ligand has inserted into the Pt–C bond of the bridging carbonyl of (1) to give a dimetallacyclopentanone ring with an exocyclic methylene group. Treatment of complex (1) with allene at 80 °C gave [(OC)3Fe(µ-dppm){µ-C(CH2)CH2}Pt(PPh3)](5) in moderate yield. The structure of (5) was also established by X-ray crystallography; the crystals are monoclinic, space group P21/n, with a= 1 195.1(2), b= 2 258.5(3), c= 1 673.9(4) pm, β= 108.15(2)°, and Z= 4; R 0.0286 for 4 835 observed reflections. The allene ligand is bridging the Fe–Pt bond to give a dimetallacyclobutane ring with an exocyclic methylene group. When complex (3) or (5) was heated at 80 °C the complex [(OC)2Fe(µ-dppm){η4-(CH2)2CPt(PPh3)}](6) was formed in high yield. Analogues of (6) were prepared by treatment of (1) with the substituted allenes PhCHCCH2 and Me2CCCH2, viz. [(OC)2Fe(µ-dppm){η4-(CH2)(CHPh)CPt(PPh3)}](7) and [(OC)2Fe(µ-dppm){η4-(CH2)(CMe2)CPt(PPh3)}](8). The structure of (8) was established by X-ray crystallography; the crystals are monoclinic, space group P21/c, with a= 1 098.4(3), b= 1 889.8(6), c= 2 216.3(5) pm, β= 103.52(2)°, and Z= 4; R 0.0311 for 5 080 observed reflections. It is most informatively viewed as a phosphine-substituted platinatrimethylenemethane complex in which the (CH2)(CMe2)CPt(PPh3)(dppm-P) moiety is η4-co-ordinated to Fe.Protonation of (5) with HBF4·OEt2 gave the µ-propenyl cation [(OC)3Fe(µ-dppm){µ-C(Me)CH2}Pt(PPh3)][BF4] exclusively. Some similar chemistry with the diphosphine (Ph2P)2CCH2 is also described.