Accelerating the insertion reactions of (NHC)Cu–H via remote ligand functionalization

Abstract

Most ligand designs for reactions catalyzed by (NHC)Cu-H (NHC = N-heterocyclic carbene ligand) have focused on introducing steric bulk near the Cu center. Here, we evaluate the effect of remote...

A Well‐Defined Anionic Dicopper(I) Monohydride Complex that Reacts like a Cluster**

“…[19,20,22,23,[26][27][28]30] As discussed above, the addition of a terminal alkyne did not lead to an insertion into the CuÀ H bond, contrary to what is observed for other dicopper hydrides. [20,22,24,27] Similarly, the addition of other unsaturated substrates to 1 (alkenes, internal alkynes, ketones, nitriles and imines) did not lead to the corresponding insertion products despite the lack of steric encumbrance around the hydride (Figure 1). Altogether, it is evident that 1 reacts distinctly different from reported dicopper hydrides.…”

“…Dicopper hydrides are known be susceptible to insertion reactions of unsaturated substrates into the Cu−H bond, hence we explored such reactivity for 1 [19, 20, 22, 23, 26–28, 30] . As discussed above, the addition of a terminal alkyne did not lead to an insertion into the Cu−H bond, contrary to what is observed for other dicopper hydrides [20, 22, 24, 27] . Similarly, the addition of other unsaturated substrates to 1 (alkenes, internal alkynes, ketones, nitriles and imines) did not lead to the corresponding insertion products despite the lack of steric encumbrance around the hydride (Figure 1).…”

“…The tendency of CuHs to form oligomers and other polynuclear complexes through electron deficient multicenter two‐electron bonding has resulted in the structural characterization of a plethora of CuH clusters [14–17] . In contrast, well‐defined low‐nuclearity CuHs are rare and especially mono‐ and dinuclear CuHs are only sporadically isolated and structurally characterized (see Table S1) [18, 19, 20–28] . In 2013 Sadighi and co‐workers showed that bulky N‐heterocyclic carbene (NHC) ligands can be exploited for the stabilization of dinuclear CuHs (Scheme 1, C ) [20, 22] .…”

“…However, the instability of low‐nuclearity CuHs and their fluxional behavior in solution have hampered mechanistic studies of these transformations. Very recently, Bullock and co‐workers reported detailed mechanistic studies on the insertion chemistry of [(NHC)Cu(μ‐H)] 2 complexes showing the importance of CuH monomerization to enable insertion of unsaturated substrates [27, 30] . However, investigations into the inherent reactivity of dinuclear monohydrides themselves are absent due to the lack of robust systems that do not change aggregation state in solution.…”

“…[20,22] Subsequently, numerous CuH complexes bearing sterically encumbering NHC ligands have been reported and employed as catalysts for the functionalization of unsaturated organic substrates. [23,[26][27][28][29][30] However, the instability of low-nuclearity CuHs and their fluxional behavior in solution have hampered mechanistic studies of these transformations. Very recently, Bullock and co-workers reported detailed mechanistic studies on the insertion chemistry of [(NHC)Cu-(μ-H)] 2 complexes showing the importance of CuH monomerization to enable insertion of unsaturated substrates.…”