Combination of alkynes with µ-carbenes at a dimetal centre, and X-ray structure of [Fe₂(CO)(µ-CO){µ-η¹,η³-C(CO₂Me)C(CO₂Me)CHMe}(η-C₅H₅)₂]: implications for metathesis and alkyne polymerisation

Abstract

Rridging methylcarbene complexes [M,(CO),-(p-CO)(p-CHMe)(q-C,H,),] (M = Fe or Ru) react with alkynes RCiR1 (R = R1 = HI Me, C0,Me; R = Me, R1 = H) under U.V. irradiation to produce complexes [M,(CO) (p-CO) (p-q1,q3-CRCR1CHMe) (q-C5H5),], shown through an X-ray diffraction study of [Fe,(CO) (p-C0)-{p-q1,y3-C (C0,Me) C (C0,Me) CHMe 1 (q-C5H5),] to arise from linking of the p-carbene and alkyne. THE chemistry of carbene complexes of transition metals has attracted much investigation, not least because of their implication in the metathesis1p2 of alkenes. Almost all study has been concerned with carbenes co-ordinated a t a mononuclear metal centre and has been associated with mechanistic schemes for metathesis based on monometallocycles. By comparison, the reactivity of carbenes coordinated a t a dinuclear metal centre ( t bridging carbenes') is effectively unexplored. Very recently, however, the possibility of metathesis involving bridging carbenes and ditungsten3 ** metallocycles has been discussed, and it has also been suggested5 that di-iron metallocycles are intermediates in the production of propene from [Fe,(CO),-(p-CH,)] and ethene. In the course of studies*--* on the reactivity of dinuclear metal centres we have developed8 a convenient synthesis of p-carbene di-iron and diruthenium complexes, and now report that these are highly reactive towards ethyne and other alkynes, forming stable dimetallocycles through carbon-carbon bond formation.The p-methylcarbene complexes [M2(C0), (p-CO) (p-CH-Me) (q-C5H5),] (1) exist in solution as cis (predominantly) and trans isomers, the cis iron complex having been found to adopt, in the solid state a t least, the anti methyl group orientation illustrated.8 Each complex (1) reacts with ethyne under U.V. irradiation (toluene solution, silica glass flask, 250 W mercury lamp, 3 and 25 h respectively) to give crystalline olive-green [Fe,(CO) (p-CO) (p-q1,q3-CHCHCH-q3-CHCHCHMe) (q-C5H,),] (2b) (55%) , respectively. No Me) ('q-c5H5)2] (2a) (85%) f or orange [Ru,(CO) (p-co) (p-qlIt (2a): m.p. 178-182 "C(decomp); v(CO)(hexane) 1 961% and 1 793m cm-l; lH n.m.r. (CDCI,) 6 11-86 (d, J 6 Hz, C4H). 4.71 (s,

Coupling of Allenes with μ‐Alkylidyne Ligands in Diiron Complexes: Synthesis of Novel Bridging Thio‐ and Aminobutadienylidene Complexes

“…The reaction selectively afforded the metallacyclo complex 6, rather than removing a proton (Scheme 8). Scheme 8. The formation of 6 is consistent with the previously reported reactions of analogous vinyliminium complexes [Fe 2 {µ-η 1 :η 3 -C γ (RЈ)C β HC α N(Xyl)(Me)}(µ-CO)(CO)(Cp) 2 ]-[SO 3 CF 3 ] (R = Me, CO 2 Me, CMe 2 OH) which, upon treatment with NaH, resulted in a similar fragmentation of the diiron compound and formation of the corresponding 1-metalla-2-amino-cyclopenta-1,3-dien-5-one complexes. [19] Complex 6 has been characterized by IR and NMR spectroscopy, as well as by elemental analysis.…”

“…The cis-4b crystals appeared to be racemically twinned with a refined Flack parameter of 0.49(4). [29] CCDC-673762 (for 3a), -673763 (for 4b), -673764 (for 5a[CF 3 …”

“…H atoms were placed in calculated positions, except for H (14) for which the two disordered images are related by an inversion centre; in this case, an occupancy factor of 0.5 was assigned to the independent image of the molecule and then it was refined anisotropically. Similar U restraints were applied to all C and O atoms in cis-4b, all C atoms in 5a[CF 3 SO 3 ]·CH 2 Cl 2 and all C and F atoms in 7a[CF 3 SO 3 ] ·0.5CH 2 Cl 2 . The cis-4b crystals appeared to be racemically twinned with a refined Flack parameter of 0.49(4).…”

“…These reactions take advantage of specific organic substrate activation due to multisite coordination and of reactivity patterns which are distinct from those of corresponding species in mononuclear complexes. [2] Within this field, the coupling of bridging alkylidyne (µ-CR) and alkylidene (µ-CR 2 ) ligands with alkynes [3] and, to a lesser extent with alkenes, [4] is well known to provide excellent routes to the synthesis of bridging C 3 hydrocarbyl ligands.…”

Dinuclear and Polynuclear Ruthenium Non-cluster Compounds

“…1 ,r; 3 -CHCHCHMe)(r/-C5H5)2] (21); other alkynes afford similar complexes. 37 In these the bridging C3 unit can be considered to be bonded either in an r? 3 -allylic mode (a), or as a vinylcarbene (b).…”