Reactions of the Doubly Bridged Bis(cyclopentadienyl) Dinuclear Molybdenum Complex (Me₂C)(Me₂Si)[(η⁵‐C₅H₃)Mo(CO)₃]₂ with a Carboxylate‐Substituted Allene

Abstract

Reaction of the doubly bridged bis(cyclopentadienyl) dinuclear molybdenum complex (Me2C)(Me2Si)[(η5‐C5H3)Mo(CO)3]2 (1) with equivalent molar amount of allene H2C=C=CHCO2Me in refluxing toluene gave four products: complex (Me2C)(Me2Si)[(η5‐C5H3)2Mo2(CO)4(μ‐η2‐η2‐HC≡CCH2CO2Me)] (3) (10 %) with a crosswise substituted alkyne bridge, η2‐η2‐HC≡CCH2CO2Me derived from a 1,3‐hydrogen shift of H2C=C=CHCO2Me, complex (Me2C)(Me2Si)[(η5‐C5H3)2Mo2(CO)2(O)2{μ‐η1‐η3‐C(CO2Me)CHCH2}] (6) (16 %) with a bridging η1,η3‐C(CO2Me)CHCH2 allylic group, and allene C–C coupled complexes (Me2C)(Me2Si)[(η5‐C5H3)2Mo2(CO)4{μ‐η3‐η3‐{MeO2CCH(CH2)C}(CHCHCHCO2Me)}](4) (7 %) and (Me2C)(Me2Si)[(η5‐C5H3)2Mo2(CO)4{μ‐η3‐η3‐{MeO2CCH(CH2)C}2}] (5) (13 %), in which the two allene molecules were coupled in head‐to‐center and center‐to‐center coupling modes, respectively. When 1 was treated with an excess amount of H2C=C=CHCO2Me, only C–C coupled products 4 (10 %) and 5 (22 %) were obtained. In comparison, reaction of the singly bridged bis(cyclopentadienyl) dinuclear molybdenum complex (Me2C)[(η5‐C5H4)Mo(CO)3]2 (2) with H2C=C=CHCO2Me only gave the η2‐η2 coordinated complex (Me2C)[(η5‐C5H4)Mo2(CO)4(μ‐η2‐η2‐H2CCCHCO2Me)] (7) (21 %). These results marked the different reactivities of doubly bridged bis(cyclopentadienyl) dinuclear molybdenum complex 1 and the corresponding singly bridged analogue 2. The formation of these complexes was discussed and the molecular structures of 3–7 were determined by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Diverse Coordination Modes and Transformations of Allenes at Adjacent Iridium/Osmium Centers

“…Allenes also exhibit a diverse coordination chemistry. Whereas these groups bind to a single metal almost exclusively in the η 2 -olefinic mode via one of the π bonds, the presence of a pair of adjacent metals introduces a number of additional modes, as outlined in Chart , for allene itself, in which either one or both sites of unsaturation can be involved in the bonding. In structure A , the allene is bound in a μ-κ 1 :κ 1 binding mode through one of the π bonds to form a dimetallacyclobutane moiety having exocyclic unsaturation .…”

Reactions of (Me2C)(Me2Si)[(η5‐C5H3)­Mo(CO)3]2 with Phosphanylalkynes: Rearrangement of Phosphanylalkynes into Phosphido‐Substituted Vinylidenyl Ligands by Cleavage of the P–C(alkyne) Bond and Formation of a P–C(alkene) Bond

“…The dimensions of the Mo 2 C 2 core are similar to those found in the (Me 2 C)(Me 2 Si)[(η 5 -C 5 H 3 ) 2 Mo 2 (CO) 4 (µ-η 2 -η 2 -HCϵCCH 2 CO 2 Me)] [9] complex and the unbridged Cp 2 Mo 2 (CO) 4 (µ-RCϵCR) analogue. [18] The alkyne ligands (21) 1.347 (7) 1.352(3) 1.380(7) C(21)-P (1) 1.742 (6) 1.761 (2) 1.746(5) Mo(1)-P (1) 2.4357 (15) 2.4477 (7) 2.4230 (14) Mo (2) (1) 93.54 (19) 92.91 (9) 93.81(19) Mo (2) (21) 93.28 (18) 93.45 (8) 94.41 (16) in these complexes are all tipped over to the CMe 2 bridge side of the doubly bridged ligand, possibly owing to the smaller steric effect of the CMe 2 bridge than that of the SiMe 2 bridge.…”

“…[8] The reaction of complex 1 with the allene H 2 C=C=CHCO 2 Me produced two allene-isomerization products and two allene-coupling products, which is significantly different from the reactivity of allene with nonbridged and singly bridged dinuclear molybdenum carbonyl complexes. [9] The N-N bond cleavage of diazoalkane Ar 2 CN 2 following orthometalation of the aryl and disproportionation of CS 2 were observed in thermal reactions with 1. [10] In this contribution, we report the reactions of complex 1 with a series of phosphanylalkynes Ph n P-(CϵCR) 3-n [n = 2, 1, 0; R = Ph, Fc (ferrocenyl, C 10 H 9 )], in which the phosphanylalkynes behaved as disubstituted acetylenes, and/or the cleavage of P-C(alkyne) bond and rearrangement of phosphanylalkynes into phosphido-substituted vinylidenyl ligand were observed.…”