“…[3d,9] However,w hereas [(6/7Dipp)Cu(m-H)] 2 prove stable for days at 298 K, 2 was stable only below 209 K. Above this temperature,t he 1 HNMR resonances began to broaden and at 255 Ks ignals for 3 were present. [11] TheX -ray structure of 5 ( Figure 1) showed the presence of at wo-coordinate Cu center attached to the carbene and amonodentate {HBEt 3 }moiety.T he hydrogen atom on B(1) was located and refined without restraint, yielding C 6Mes -Cu-Ha nd Cu-H-B angles of 162.4 (13) and 110.2(18)8 8,r espectively,and B-H and Cu-H distances of 1.22(3) and 1.56(3) , respectively.T he latter is comparable to the shortest Cu-H distance in II, [3b] but much shorter than either of the Cu-H bond lengths in III (1.679(2) ,1 .717 (18) ). [3b] Unsurprisingly,e xamples of isolable triethyl-borohydride complexes are rare,b eing confined to very electropositive metals.…”