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.