Activation of propargylic alcohols by dimolybdenum tris(mu-thiolate) complexes: Influence of the substituents R in HC CCR2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes

Ojo, W. S., Capon, J. F., Le Goff, A., Petillon, F. Y., Schollhammer, P., Talarmin, J. and Muir, K. W. (2007) Activation of propargylic alcohols by dimolybdenum tris(mu-thiolate) complexes: Influence of the substituents R in HC CCR2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes. Journal of Organometallic Chemistry, 692(24), pp. 5351-5367. (doi: 10.1016/j.jorganchem.2007.08.023)

Abstract

Reaction of the bis(nitrile) complex [Mo2Cp2(mu-SMe)(3)(NCMe)(2)](BF4) ( 1) with dimethylpropargylic alcohol, HC CCMe2(OH), at room temperature in dichloromethane produced good yields of the mu-alkynol species [Mo2Cp2(mu-SMe)(3){mu-CHCCMe2(OH)}](BF4) (2a) through replacement of the two acetonitrile ligands in 1 by the alkynol. The NMR spectra of 2a indicate a l-g 1: g 1 coordination mode for the alkyne which is thereby incorporated into a dimetallacyclobutene ring like that found here by X-ray diffraction (XRD) analysis of the related complex [Mo2Cp2(mu-SMe)(3)(mu-eta(1):eta(1)-CHCCO2Me)](BPh4) (2b). When 2a was stirred with Et3N at room temperature in dichloromethane, deprotonation gave high yields of the mu-3-hydroxyalkynyl derivative [Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(2)-CCCMe2(OH)}] (3), together with small amounts of the already-known vinylacetylide [Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(2)-CCC(Me)CH2}] (4) resulting from dehydration of 3. Treatment of 3 with 1 equiv. of HBF4 OEt2 in diethyl ether at room temperature gave the 3-hydroxyvinylidene derivative [ Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(2)-CCHCMe2(OH)}](BF4) (5) as the major product, together with other minor products [Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(2)-CCHC(Me) CH2}](BF4) (6), [Mo2Cp2(mu-SMe)(3)(mu-eta(1):eta(2)-CCCMe2)]( BF4) (7), [ Mo2Cp2(mu-SMe)(3)(mu-eta(1):eta(CCH2)-C-2)]( BF4) (8), [Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(2)-CCH(CHMe2)}](BF4) (9) and [Mo2Cp2(mu-SMe)(3)(mu-O)](BF4) (10). The vinylidene (6) and allenylidene (7) species resulted from dehydration of the 3-hydroxyvinylidene complex 5 whereas the vinylidene derivative 8 was formed by deketonisation of 5. When 3 reacted with a large excess of HBF4 center dot OEt2 in dichloromethane, the 3-isopropylvinylidene complex 9 was obtained nearly quantatively via a H-center dot radical process. When left for several days CD2Cl2 solutions of 5 afforded mainly the vinylidene species 8 by deketonisation and the side-oxoproduct [Mo2Cp2(mu-SMe)(3)(mu-O)](BF4) (10) by hydrolysis or reaction with oxygen. Addition of nucleophiles (H-, OMe-, OH-, SMe-) to the allenylidene complex [Mo2Cp2(mu-SMe)(3)(mu-eta(1):eta(2)-CCCPh2)](BF4) (11) resulted in the formation of the corresponding mu-acetylide derivatives [Mo2Cp2(mu-SMe)(3)(mu-eta(1):eta(2)-CCCRPh2)][R = H (12), OMe (16a), OH (17), SMe (16b)], which by further reaction with tetrafluoroboric acid afforded either the vinylidene species [Mo2Cp2(mu-SMe)(3){mu-eta(1):eta(CH)-C-2( CRPh2)}](BF4) when R = H (13), or the starting complex 11 when R is a leaving group (OMe). Reaction of 13 with Na(BH4) gave the mu-alkylidyne complex [Mo2Cp2(mu-SMe)(3)(mu-eta(1)-CCH2CPh2H)] (14) by nucleophilic attack of H- at the C-beta carbon atom of the vinylidene chain. Proton addition at C-alpha in 14 led to the formation of a mu-vinylidene compound 15 containing an agostic C-H bond. New complexes have been characterised by elemental analyses and spectroscopic methods, supplemented for 2b and 3 by X-ray diffraction studies. .

• Item Type: Articles
• Keywords: 2-PROPYN-1-OL DERIVATIVES Acetonitrile ACETYLIDE COMPLEXES ACID ACTIVATION ALCOHOLS alpha-Agostic BOND C BOND-CLEAVAGE C-H C-H BOND CARBON CHAIN COMPLEX COMPLEXES COORDINATION CRYSTAL-STRUCTURES DERIVATIVES DIFFRACTION dimolybdenum complexes ELECTROCHEMICAL REDUCTION HYDROLYSIS LIGAND LIGANDS mu-Acetylide,mu-3-hydroxyvinylidene,mu-3-isopropyl,mu-alkylidyne,mu-alkylidene species NMR NMR-SPECTRA NUCLEOPHILIC-ADDITION POLYNUCLEAR METAL-COMPLEXES PRODUCTS propargylic-alcohol activation REACTIVITY RICH BIMETALLIC SITE RING ROOM-TEMPERATURE SPECTRA spectroscopic methods SPECTRUM SUBSTITUENTS TEMPERATURE TERMINAL ALKYNES thiolato-bridged complexes TRANSFORMATION VINYLIDENE COMPLEXES X-RAY X-ray diffraction X-RAY-DIFFRACTION XRD
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Muir, Dr Kenneth
• Authors: Ojo, W. S., Capon, J. F., Le Goff, A., Petillon, F. Y., Schollhammer, P., Talarmin, J., and Muir, K. W.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Organometallic Chemistry
• ISSN: 0022-328X