Synthesis, Properties, and Structure of Tethered Molybdenum Alkylidenes

Abstract

A new class of molybdenum alkylidenes has been prepared where the alkylidene is tethered to an imido ancillary ligand. The amine required for the synthesis is accessible in 38% yield in five steps from 1,3-diisopropylbenzene. The amine is then installed to generate the tethered alkylidene bis(triflate) complex, which was structurally characterized as its DME adduct. The triflates are replaced by hexafluoro-tertbutoxide groups using the thallium salt of the alkoxide, and the bis(alkoxide) was characterized as its quinuclidine adduct. For comparison, an alkylidene bis(alkoxide) was prepared without the tether and having a formula similar to that of the tethered system. The structures from X-ray diffraction and NMR spectroscopy of the two complexes with and without the tether but with similar formulas are compared. The tether has the apparent effect, judging from J CH couplings in the alkylidene and angles in the solidstate structure, of reducing the strength of the R-agostic interaction. Four complexes were structurally characterized during this study: 4-Pr i 2 C 6 H 2 -2-CH 2 CH 2 CMe 2 CHd](DME)(OTf) 2 , Mo(OBu t F6 ) 2 (quin)-[dN-2,4-Pr i 2 C 6 H 2 -2-CH 2 CH 2 CMe 2 CHd], Mo[N(2,4-Pr i 2 -6-MeC 6 H 2 )] 2 (neopentyl) 2 , and Mo(OBu t F6 ) 2 (quin)-[N(2,4-Pr i 2 -6-MeC 6 H 2 )][dC(H)Bu t ].

C−H Activation for the Construction of C−B Bonds

“…Finally, Odom and co-workers have used this C-H borylation and cross-coupling sequence to prepare ligands for transition metal complexes. 209 They reported the borylation of 1,3-iPr 2 C 6 H 4 catalyzed by (Ind)Ir(COD) and dmpe at 130 °C as the initial step in their multistep synthesis of 6-(3,3-Me 2 -pent-4-enyl)-2,4-iPr 2 -aniline. This ligand was then used to prepare a tethered molybdenum alkylideneimine-bis(alkoxide) catalyst for olefin metathesis.…”

1,2-CF bond activation of perfluoroarenes and alkylidene isomers of titanium. DFT analysis of the C–F bond activation pathway and rotation of the titanium alkylidene moiety

“…To prohibit the interconversion of syn and anti isomers in solution the groups of Fürstner [7,8] and Grubbs [9,10] prepared tethered ruthenium carbene complexes with carbene ligands connected to an N-heterocyclic carbene. Odom reported the only examples of earlytransition metal alkylidene complexes tethered to the adjacent imido ligand (Schrock-type catalysts) [11].…”

Highly Tactic Cyclic Polynorbornene: Stereoselective Ring Expansion Metathesis Polymerization of Norbornene Catalyzed by a New Tethered Tungsten-Alkylidene Catalyst

“…Grubbs’ ring expansion metathesis polymerization (REMP) strategy overcomes some of the challenges in cyclic polymer synthesis . REMP utilizes a cyclometalated alkylidene metal complex as the catalyst. , In this case, the two ends of the growing polymer remain attached to the metal throughout the polymerization process, thus releasing a cyclic polymer upon intramolecular chain transfer . Cyclic dendronized polymers and cyclic brush polymers employing norbornene-based macromonomers were synthesized via REMP using cyclic ruthenium catalysts; however, control over both tacticity and the cis / trans ratio is either not reported or absent.…”