Synthesis of Unsymmetrical Diolate, Oxametallacyclopentene, Amido-Alkoxide and Thiolato-Alkoxide Complexes Using Dialkyl and Diaryl Titanium Aminotroponiminate Complexes:  A Route to Unsymmetrical Vicinal Diols

Abstract

The reactivity of [TiR2(Me2ATI)2] complexes, where Me2ATI = N,N ‘-dimethylaminotroponiminate, or L, with CO or RNC in the presence of various organic electrophiles has been investigated. The compounds TiMe2L2 and TiPh2L2 react with CO and aldehydes or ketones to afford unsymmetrical diolate complexes that convert to the corresponding vicinal diols after hydrolysis. Phenyl acetylene also reacts to form the oxametallacyclopentene complex [Ti(OCMe2CHCPh)(Me2ATI)2]. Treatment of TiMe2L2 with RNC yields the free imine and a source of low-valent titanium. Trapping this intermediate with 2 equiv of benzaldehyde or benzil affords the titanium diolate or enediolate complex, respectively. When 1 equiv each of benzophenone and either N-tosylbenzaldimine or acetone were added to the intermediate, [Ti(Ph2COCN(SO2tol)HPh)(Me2ATI)2] and [Ti(Ph2COCOMe2)(Me2ATI)2], respectively, were obtained. The titanium thiolato-alkoxide complex [Ti(Ph2CSCOMe2)(Me2ATI)2] was prepared by use of thiobenzophenone and acetone. This chemistry allows for the preparation of unsymmetrical diols and oxametallacyclopentene complexes from Ti(IV) dialkyls, CO, and either carbonyl compounds or alkynes. Amido-alkoxide and thiolato-alkoxide complexes can be prepared by the reaction of Ti(IV) dialkyl complex, 2 equiv of benzophenone, and either an imine or thioketone.

Low-Valent Titanium-Mediated Reductive Coupling of Carbonyl Compounds

“…A carbonyl insertion pathway for formation of titanapinacolate complexes is further supported by observation of putative η 2 -carbonyl complexes in reactions of 64 with benzaldehyde and p-chlorobenzaldehyde. The formation of unsymmetrically substituted titanapinacolate complexes from reaction of L 2 TiR 2 complexes (R = Me or Ph; L = N,N'-dimethylaminotroponiminate) with CO and aldehydes or ketones was also proposed to proceed via a reactive titanium-η 2 -carbonyl intermediate, formed by double alkyl migration to CO [131]. Titanapinacolates have also been isolated from reactions of carbonyl compounds with cyclopentadienyl compounds, Cp 2 Ti(CO) 2 and CpTiX 2 (THF) 2 (X =Cl, Br) [132].…”

The McMurry Coupling and Related Reactions

“…Unsymmetrical diolate complexes have been obtained by treatment of the dialkyl or diaryl complexes L 2 TiR 2 (R ¼ Me or Ph, L ¼ N,N 0 -dimethylaminotroponiminate) with CO and aldehydes or ketones; a reactive titanium h 2 -carbonyl compound, formed by double alkyl migration to CO, was proposed as a key intermediate in these reactions [272]. tBuCcCH, which revealed that the fragmentation reactions proceed via a preequilibrium mechanism giving (DMSC)Ti(h 2 -OCAr 2 ) and Ar 2 CO, followed by ratelimiting reaction of (DMSC)Ti(h 2 -OCAr 2 ) with the alkyne molecule [273].…”

Multiple bridging modes in a novel trinuclear titanium 1,3-dioxypropane compound, Ti3(methyliminodiethanolate)2(1,3-propanediolate)4

“…In the related ®ve-coordinate [Ti(2,4-dimethyl-2,4-pentanediolate) 2 ] 2 dimer, the TiÐO lengths range from 1.802 (2) to 1.816 (2) A Ê (Damo et al, 2000). In six-coordinate titanium complexes with unsymmetrically substituted neutral glycols (Steinhuebel & Lippard, 1999), the TiÐO distances are comparable, varying from 1.862 (4) to 1.888 (2) A Ê .…”