Synthesis, Characterization, and Catalytic Activity of Bimetallic Ti/Cr Complexes

Abstract

We report herein the reactions of the Rosenthal complexes, Cp2Ti­(BTMSA) and Cp*2Ti­(BTMSA) (BTMSA: bis­(trimethylsilyl)­acetylene), with CpCr­(CO)3H. Those complexes are known to dissociate their alkyne ligands and to exhibit the reactivities of the putative titanocenes “Cp2Ti” and “Cp*2Ti”. Our reactions appear to proceed through the addition of CpCr­(CO)3H to these titanocenes, giving rise to TiIV-H intermediates that lose H2 to form the TiIII–Cr complexes 1 and 2. In the solid state, 1 and 2 both adopt a dimeric geometry, involving a 12-membered “Ti2Cr2” ring held together with Ti–O–C–Cr bridging carbonyls. The terminal carbonyls in 1 and 2 are trans. DFT calculations confirm that the loss of H2 from the TiIV-H intermediateforming the TiIII-Cr dimeris exergonic by 14.2 kcal mol–1 in the gas phase. The Bercaw compound Cp* (C5Me4CH2)­TiCH3 reacts with CpCr­(CO)3H to form a TiIV-CH3 species with a coordinated CpCr­(CO)3 – anion (3). The Ti-Cr dimer 1 is capable of catalyzing the hydrogenation of an epoxide to an anti-Markovnikov alcohol, avoiding the use of Cp2TiX2 (X = Cl– or mesylate), NaCpCr­(CO)3, and HCpCr­(CO)3 separately as in our previous catalyst system.

A Programmable Synthesis of Diverse Terpene Architectures from Phenols

“…As shown in Figure 2, in all cases examined (see SI for the synthesis of the prenylated starting materials) the para-Claisen rearrangement performed well using 22 as the preferred promoter. The conditions were mild enough that TBS-protected primary alcohols (34)(35)(36), TMS-protected tertiary alcohols (32), Boc-protected amines (38), and even free alcohols (46) were tolerated. Aryl halides worked as well, affording vinylic halide products 30 and 31, as did the 4-membered ring of 32 (which can potentially afford a spirocyclic system after a semi-pinacol rearrangement).…”

Latest News: Reactions of Group 4 Bis(trimethylsilyl)acetylene Metallocene Complexes and Applications of the Obtained Products

“…Norton and coworkers published reactions of the titanium bis(trimethylsilyl)acetylene complexes Cp 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 ) and Cp* 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 ) with CpCr(CO) 3 H (Scheme 11). [13a] As mentioned before, in these complexes the alkyne dissociates and thus the reactivities of titanocene complexes [Cp 2 Ti] and [Cp* 2 Ti] were studied. With CpCr(CO) 3 H, an addition to form Ti IV ‐H intermediates followed by loss of H 2 under formation of bimetallic Ti III ‐Cr complexes was described.…”

“…Upon coordination of solvents like CH 3 CN, the observed solvatochromic shifts of the two tetranuclear Ti 2 Cr 2 compounds indicate the breakdown of the dimeric structures (Scheme 13). [13a] …”

“…The above‐mentioned 12‐membered heterobimetallic Ti III ‐Cr complexes showed activity as catalysts for the hydrogenation of an epoxide to yield an anti‐Markovnikov alcohol (Scheme 14). [13a] This was possible without the use of Cp 2 TiX 2 (X=Cl, mesylate), NaCpCr(CO) 3 , and HCpCr(CO) 3 as described in previous catalytic systems from the authors.…”