Recent advances in the development of alkyne metathesis catalysts

Abstract

SummaryThe number of well-defined molybdenum and tungsten alkylidyne complexes that are able to catalyze alkyne metathesis reactions efficiently has been significantly expanded in recent years.The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review.

Synthesis and characterization of a trianionic pincer supported Mo-alkylidene anion and alkyne insertion into a Mo(IV)-C bond to form metallocyclopropene(η2-vinyl) complexes

“…The molybdenum ion is coordinated by (17) (except two (1.342(6) Å) [55] and 1.263(2) Å [56]) is the C27eC28 bond length of 1.420(3) Å for the CeC bond in 10-H. Interestingly, the phenyl ring attached to C28 is coplanar with the metallocyclopropene, suggesting conjugation exists between them. The central aryl ring of the diphenolate ligand is one of the metallocyclopropene substituents and creates considerable strain on the C27 atom creating angles of Mo1eC27eC12 ¼ 88.30(11), C28eC27eC12 ¼ 124.13 (17), and C28eC27eMo1 ¼ 62.28 (10) . Deviations from archetypical [46,47] Mo-derivatives are the small Mo1eC27eC12 (normally 115(2) ) and the large C28eC27eMo1 angle (normally 57.7(2) ).…”

Phosphoraneiminato tungsten alkylidyne complexes as highly efficient alkyne metathesis catalysts

“…Thus, an initial turnover frequency (TOF) of ca. 45 min À1 can be calculated for 3a and 3b for the first 2 min reaction period, revealing the presence of exceptionally active catalysts [8,9]. These activities suggest that the reaction could also be performed with significantly lower catalyst loadings, and a preliminary study at 0.1 mol% catalyst loading involving 5 mmol of 3a, 5 mmol of 4, 1.0 g of MS 5 Å and 5 mL of toluene afforded the alkyne 5 in 85% yield after 6 h reaction time; full conversion was not achieved within 24 h. Future work will focus on the optimization of the reaction conditions.…”

“…In particular, significant efforts were made to establish alkylidyne complexes as homogeneous catalysts for applications in alkyne metathesis and to develop catalyst systems that live up to expectations with regard to their activity, substrate compatibility, and required reaction temperature [8]. More recently [9], a number of new tungsten-and molybdenum-based catalysts were introduced that rely on the use of ancillary imidazolin-2-iminato [10,11], silanolate [12,13], or chelating polyphenolate ligands [14]; our own main contribution to this field comprises the preparation of imidazolin-2-iminato neopentylidyne and benzylidyne complexes [RC^M(NIm tBu …”

Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

“…In Route 1, the chloride ligand in (Me 3 CCH 2 ) 4 TaCl (20) is replaced first to give penta-alkyl complex Ta(CH 2 CMe 3 ) 5 (21), followed by a-H abstraction to give the alkylidene 5a. In Route 2, (Me 3 CCH 2 ) 4 TaCl (20) undergoes a-H abstraction first to give the alkylidene ligand in "(Me 3 CCH 2 ) 2 Ta(] CHCMe 3 )Cl" (22), followed by the Cl À substitution to yield 21. In other words, the key question is whether the Ta]C bond forms before or after the Cl À substitution.…”