Alkene to Carbyne: Tandem Lewis Acid Activation and Dehydrogenation of a Molybdenum Ethylene Complex

Abstract

Carbyne formation: Treatment of a molybdenum ethylene complex with B(C6 F5 )3 induces ditopic activation of an ethylene ligand and acceptor-assisted ethane elimination to generate a novel type of zwitterionic carbyne complex.

Group 6 Transition‐Metal/Boron Frustrated Lewis Pair Templates Activate N2and Allow its Facile Borylation and Silylation

“…The 31 PNMR spectra of 3 Mo and 3 W display asingle peak shifted downfield to 73.1 ppm and 69.2 ppm, respectively (vs.6 5.2 for 1 Mo and 46.1 for 1 W ). 11 Ba nd 19 FNMR spectra are in accordance with the formation of adducts of borane 2 (shielding of the para fluorine atoms and an egative boron chemical shift, see the Supporting Information Figures S1-4 and S6-9). Repeating these experiments on al arger scale in toluene or chloroben- ]a nd long N À Nd istances [1.196(5) for 3 Mo and 1.212(6) for 3 W vs.1.096 for free N 2 and 1.10(2) for 1 Mo ]s upport aM =N=Nd epiction, [16] as ar esult of enhanced metal-to-N 2 back bonding.T he BÀNb onds are 1.567 (7) (3 Mo )a nd 1.570(6) (3 W )a nd fall within the range of B À N bond lengths typical of classical adducts of 2 with nitrogen bases.…”

“…Ther eactions of the dark green complexes 3 with 1equivalent of triethylsilane (6)i n[ D 8 ]toluene or with al arge excess of neat triethylsilane (6)a tr oom temperature resulted in ac olor change to dark red. Again, 11 BNMR analysis of the isolated solids in C 6 D 6 suggested the formation of the [HB(C 6 F 5 ) 3 ] À anion (doublet around À24.5 ppm). 1 HNMR showed the disappearance of the SiHEt 3 signal and the appearance of eight shielded aromatic ortho protons.…”

“…dinitrogen complexes.T his choice was because as ubstantial body of work exists on their reactivity, [10] and the Group 6 M(dppe) 2 platforms have shown interesting reactivity regarding the activation of small organic fragments that is reminiscent of FLP chemistry. [11] We surmised that 1 could react with the strong electrophile tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 , 2)a nd trigger formal reduction of the N 2 ligand, akin to protonation. [12] While this paper was being written, Szymczak and co-workers reported, in av ery elegant but contextually different study,t hat adduct formation of 2 with the [(depe) 2 Fe(N 2 )] complex (depe = 1,2-bis(diethylphosphino)ethane) enhances activation of the dinitrogen ligand (Scheme 1, bottom).…”

Group 6 Transition‐Metal/Boron Frustrated Lewis Pair Templates Activate N2and Allow its Facile Borylation and Silylation

“…[13] We treated orange C 6 D 6 suspensions of 1 with 1equivalent of 2 at room temperature and immediately obtained dark green solutions.S pectroscopic analysis indicated the clean formation of new complexes 3, according to 1 H, 31 P, 19 Fand 11 BNMR spectroscopy (! 11 Ba nd 19 FNMR spectra are in accordance with the formation of adducts of borane 2 (shielding of the para fluorine atoms and an egative boron chemical shift, see the Supporting Information Figures S1-4 and S6-9). The 1 HNMR spectra show inequivalent sets of methylene and aromatic protons,w hich indicates al oss of symmetry.E ight aromatic ortho protons are particularly shifted to high field.…”

Frustrated Lewis Pairs

“…179 This situation is highly reminiscent of bifunctional transition metal catalysts. In this regard it is also important to draw attention to transition metal based FLPs in which metal centers with pendant donors activate a range of small molecule substrates, which has been explored by the groups of Wass [126][127][180][181][182][183] and Erker 128-129,184-188 among others. 130 The concept of FLPs has also been exploited to describe a variety of systems that activate small molecules.…”