HEAD TO HEAD ACETYLENE COUPLING AT A HETEROBIMETALLIC CENTER TO GIVE A RHODACYCLOPENTADIENE IRON UNIT - SYNTHESES AND X-RAY CRYSTAL-STRUCTURES OF (TERT-BU2PH)(CO)2FE(MU-CO)(MU-TERT-BU2P)RH(COD)(FE-RH), (CO)2FE(MU-TERT-BU2P)(MU-ETA-4-C4H2(PH)2)RH(HCCPH)(FE-RH), AND RH2FE(CO)3(TERT-BU2PH)(MU-CO)2(MU-TERT-BU2P)2

Reaction of Fe(CO)3(t-Bu2PH)(t-Bu2PLi), generated in situ from Fe(CO)3(t-Bu2PH)2and n-BuLi, with [Rh(COD)Cl]2(COD = 1,5 cyclooctadiene)) gives the heterobimetallic, di-tert-butylphosphido-bridged complex (t-Bu2PH)(CO)2Fe(μ-CO)(μ-t-Bu2P)Rh(COD)(Fe-Rh) (1) (30%). The molecular structure of 1 contains a single Fe-Rh bond that is bridged by a di-tert-butylphosphido unit. The coordination geometry about Fe is roughly trigonal bipyramidal with one CO ligand occupying a semibridging site to the Rh atom. The t-Bu2PH ligand is trans to the t-Bu2P-unit. The coordination geometry about Rh is roughly square-planar. 1 reacts with phenylacetylene (2.5 equiv) in THF under reflux (2 h) to give dark red (CO)2Fe(μ-t-Bu2P)(μ-η4-C4H2Ph2)Rh(HCCPh)(Fe-Rh) (2) in 70% yield. The C4H2Ph2unit is formed from the head to head coupling of two acetylene units and stradles the Fe-Rh bond so that the RhC4unit is virtually planar and equivalent to a metallacyclopentadiene group in its bonding to Fe. The Fe atom bears two terminal CO ligands and, including its bonding to the P atom of the μ-t-Bu2P-group, has a three-legged piano stool coordination geometry. The Rh atom also bears an η2-phenylacetylene unit. Heating 1 under reflux in acetonitrile produces Rh2Fe(CO)3(t-Bu2PH)(μ-CO)2(μ-t-Bu2P)2(3) (22%) in addition to minor amounts of [Rh(CO)(t-Bu2PH)]2(μ-H)(μ-t-Bu2P) (ca. 5%) and (CO)(t-Bu2PH)Rh(μ-t-Bu2P)Fe(CO)4(ca. 5%). The molecular geometry of 3 consists of a Rh2Fe triangle in which two t-Bu2P units bridge an Fe-Rh and the Rh-Rh bond. Two CO groups bridge the remaining Fe-Rh bond. One Rh atom bears a t-Bu2PH group and the other a terminal CO ligand. The Fe atom bears two terminal CO ligands. Crystal data for 1: C27H46FeO3P2Rh; Mr639.37; monoclinic; Cc (No. 9); a = 8.735 (2) A, b = 22.720 (3) A, c = 30.485 (4) A, β = 98.28 (2)°; V = 5987.2 (5) A3Dcalcd= 1.419 g cm-3; Z = 8; μ(Mo Ka) = 11.57 cm-1. Refinement of 2863 reflections (I > 3σ (I)) out of 5122 unique observed reflections (2° < 2θ< 48°) gave R and Rwvalues of 0.0667 and 0.0730, respectively. Data/parameter ratio = 8.47, hydrogen atoms not located. Crystal data for 2: C34H36FeO2PRh; Mr666.39; triclinic; PI (No. 2); a = 10.073 (2) Å, b = 12.785 (3) Å, c = 12.955 (3) Å, a = 97.715 (2)°, β = 105.69 (2)°, ϒ= 101.800 (2)°; V = 1540.2 (5) Å3; Dcalcd= 1.437 g cm-3; Z = 2; μ (mo Ka) = 10.764 cm-1. Refinement of 3073 reflections (I ′ 3σ (I)) out of 4829 unique observed (3° < 2θ< 48°) gave R and Rwvalues of 0.0560 and 0.0654, respectively. Data/parameter ratio = 6.402. Crystal data for 3: C29H55FeO5P3Rh2; Mt838.34; monoclinic; P21/n (No. 1014), a = 13.222 (4) Å, b = 17.940 (4) Å, c = 16.299 (6) Å, β = 104.76 (3)°; V = 3738.6 (5) Å3; Z = 4; Dcalcd= 1.489 g cm-3; μ(mo Ka) = 14.002 cm-1. Refinement of 2061 reflections (I > 3σ(I)) out of 3956 unique observed (3° <2θ< 48°) gave R and Rwvalues of 0.0820 and 0.0885, respectively. Common to all three structures: radiation (Mo Ka) 0.71073 Å (graphite monochromator). Methods: MULTAN; difference Fourier; full-matrix least squares. © 1987, American Chemical Society. All rights reserved.