Trialkylboron/Lanthanide Metallocene Hydride Chemistry:  Polydentate Bridging of (HBEt₃)^- to Lanthanum

Abstract

The reaction of [(C(5)Me(5))(2)LaH](x) with BEt(3) is reported, and the solid-state structures of the lanthanum product (C(5)Me(5))(2)La[(mu-H)(mu-Et)(2)BEt], 1, and its THF adduct (C(5)Me(5))(2)La(THF)[(mu-H)(mu-Et)BEt(2)], 2, are compared with that of the hydride-bridged "tuckover" complex (C(5)Me(5))(2)La(mu-H)(mu-eta(1):eta(5)-CH(2)C(5)Me(4))La(C(5)Me(5)), 3.

Experimental and Computational Studies of the Copper Borate Complexes [(NHC)Cu(HBEt3)] and [(NHC)Cu(HB(C6F5)3)]

“…[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.…”

“…These indicate asignificantly stronger H-B(C 6 F 5 ) 3 bond in 6 (DG 1 =+38.2 kcal mol À1 )compared to the H-BEt 3 bond in 5 (DG 1 =+10.8 kcal mol À1 ). [6] The 11 BNMR spectrum showed resonances at d = 60, 52 and À14 ppm suggestive of multiple boron-containing species being produced. TheB H 3 moiety in III is also strongly bound (DG 1 = + 36.9 kcal mol À1 ), consistent with the isolation of the borohydride complex.…”

“…[10] Upon reacting ( Unsurprisingly,e xamples of isolable triethyl-borohydride complexes are rare,b eing confined to very electropositive metals. [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) ). Additional characterization of 5 was performed in solution at low temperature (209 K).…”

“…However,n one of the signals matched those of 4. [6] The 11 BNMR spectrum showed resonances at d = 60, 52 and À14 ppm suggestive of multiple boron-containing species being produced. There was no reaction between 6 and the alkyne over days at room temperature,w ith only the transformation to the homoleptic cationic bis-carbene complex 7 apparent from the 11 BNMR spectrum.…”

Synthesis and characterization of rare examples of stable potassium and arylcalcium triethylboranate complexes

“…Baudry and coworkers studied the steric and electronic control of the stability of organolanthanide alkylborohydrides [20,21] and furthermore, some complexes were structurally characterized such as e.g. [(dipp-nacnac) Sm{(μ-H)BEt 3 }NH-C 6 H 2 -2,4,6-t Bu 3 ] [22], [(C 5 Me 5 ) 2 La{(μ-H)(μ-Et 2 ) BEt}] and [(C 5 Me 5 ) 2 La(thf){(μ-H)(μ-Et)BEt 2 }] [23].…”