1,1-Hydroboration and a Borane Adduct of Diphenyldiazomethane: A Potential Prelude to FLP-N2 Chemistry.

Diphenyldiazomethane reacts with HB(C6 F5 )2 and B(C6 F5 )3 , resulting in 1,1-hydroboration and adduct formation, respectively. The hydroboration proceeds via a concerted reaction involving initial formation of the Lewis adduct Ph2 CN2 BH(C6 F5 )2 . The highly sensitive adduct Ph2 CN2 (B(C6 F5 )3 ) liberates N2 and generates Ph2 CB(C6 F5 )3 . DFT computations reveal that formation of Ph2 CN2 B(C6 F5 )3 from carbene, N2 , and borane is thermodynamically favourable, suggesting steric frustration could preclude carbene-borane adduct formation and affect FLP-N2 capture.

Bulky derivatives of boranes, boronic acids and boronate esters via reaction with diazomethanes.

Reactions of the perfluoroarylboranes RB(C(6)F(5))(2) (R = C(6)F(5), Ph, Cl, OC(6)F(5)) with Me(3)SiCH(N(2)), (C(6)F(5))CH(N(2)) or Ph(2)C(N(2)) yield (C(6)F(5))(2)B(Me(3)SiCH(C(6)F(5))) 1, (C(6)F(5))B(Me(3)SiCH(C(6)F(5)))(2) 2, (C(6)F(5))B(Me(3)SiCH(C(6)F(5)))(Me(3)SiCH(C(6)H(5))) 3, (C(6)F(5))(2)B(CH(C(6)F(5))(2)) 4, ClB(C(6)F(5))(Ph(2)C(C(6)F(5))) 5 and (C(6)F(5)O)B(C(6)F(5))(Me(3)SiCH(C(6)F(5))) 6 as a result of single or double insertion of a Me(3)SiCH, C(6)F(5)CH or Ph(2)C fragment into a B-C bond of the respective borane. Reactions of one or two equivalents of ethyl α-diazomethylacetate with B(C(6)F(5))(3) yielded (Me)(C(6)F(5))(C=C)(OC(2)H(5))(OB(C(6)F(5))(2)) 8 and [(Me)(C(6)F(5))(C=C)(OC(2)H(5))](2)(O(2)B(C(6)F(5))) 9, in addition to the corresponding pyridine adducts (Me)(C(6)F(5))(C=C)(OC(2)H(5))(OB(C(6)F(5))(2))(py) 10 and [(Me)(C(6)F(5))(C=C)(OC(2)H(5))](2)(O(2)B(C(6)F(5)))(py) 11. Similarly, reaction of α-diazomethylacetate with BPh(3) yielded analogous products of borane reorganization, (Me)(C(6)H(5))(C=C)(OC(2)H(5))(OBPh(2)) 12 and was isolated as a mixture of E and Z-isomers whereas BPh(3) reacts with Me(3)SiCH(N(2)) and pyridine yielding (py)B(Ph(2)(Me(3)SiCH(Ph)) 7. Reactions of Ph(2)C(N(2)) with RB(OH)(2) (R = C(6)F(5), p-F-C(6)H(4), C(6)H(5)) yielded cyclic boroxines of the form [Ph(2)C(R)BO](3) (R = C(6)F(5) 13, p-FC(6)H(4) 14, C(6)H(5) 15) while reactions of the boronate esters (C(6)H(4)O(2))BR (R = C(6)F(5), p-F-C(6)H(4)) with three or five equivalents of Me(3)SiCH(N(2)) yielded (C(6)H(4)O(2))B(Me(3)SiCH(Ar)) (Ar = C(6)F(5) 16, p-F-C(6)H(4) 17) and [(Py)B(C(6)H(4)O(2))(Me(3)SiCH(Ar))] (Ar = C(6)F(5) 18, p-F-C(6)H(4), 19) upon complexation with pyridine. Reaction of HBCat and ClBCat with Ph(2)C(N(2)) yielded the products of B-H and B-Cl bond derivatization (C(6)H(4)O(2))B(Ph(2)CR) (R = H 20, Cl 21), while the triethylphosphine oxide adduct (Et(3)PO)B(C(6)H(4)O(2))(CPh(2)Cl) 22, is readily isolable.

Exchange chemistry of tBu3P(CO2)B(C6F5)2Cl.

Halide exchange from the species tBu(3)P(CO(2))B(C(6)F(5))(2)Cl 1 with Me(3)SiOSO(2)CF(3) gave tBu(3)P(CO(2))B(C(6)F(5))(2)(OSO(2)CF(3)) 2. Similarly, Lewis acid exchange occurs in reactions of 1 with Al(C(6)F(5))(3) and [Cp(2)TiMe][B(C(6)F(5))(4)] affording the products, tBu(3)P(CO(2))Al(C(6)F(5))(3)3 and [tBu(3)P(CO(2))TiCp(2)Cl][B(C(6)F(5))(4)] 4.

CO2 and formate complexes of phosphine/borane frustrated Lewis pairs.

The reaction of a solution of B(C6F4H)3 and either iPr3P or tBu3P with CO2 afforded the species R3P(CO2)B(C6F4H)3 (R=iPr (1), tBu (2)). In a similar fashion the boranes, RB(C6F5)2 (R=hexyl, cyclohexyl (Cy), norbornyl), ClB(C6F5)2, or PhB(C6F5)2 were combined with tBu3P and CO2 to give the species tBu3P(CO2)BR(C6F5)2 (R=hexyl (3), Cy (4), norbornyl (5), Cl (6), Ph (7)). Similarly, the compounds [tBu3PH][RBH(C6F5)2] (R= hexyl (8), Cy (9), norbornyl (10)) were prepared by reaction of the precursor frustrated Lewis pair (FLP) with H2. Subsequent reactions of 9 and 10 with CO2 afforded the species [((C6F5)2BR)2(µ-HCO2)][tBu3PH] (R= Cy (11), norbornyl (12)). In related chemistry, combinations of the boranes RBG(C6F5)2 (R=hexyl, Cy, norbornyl) with tBu3P treated with an equivalent of formic acid gave [(C6F5)2BR(HCO2)][tBu3PH] (R=hexyl (13), Cy (14), norbornyl (15)). Subsequent addition of an additional equivalent of borane provides a second synthetic route to 11 and 12. Crystallographic studies of compounds 2-6 and 8-14 are reported and discussed. Further understanding of the FLP complexation and activation of CO2 is provided by computational studies.

Probing substituent effects on the activation of H(2) by phosphorus and boron frustrated Lewis pairs.

The impact of substituent changes on phosphorus and boron-containing frustrated Lewis pairs (FLPs) has been examined. The phosphites (RO)(3)P R = Me, Ph form classical Lewis acid-base adducts of the formula (RO)(3)PB(C(6)F(5))(3) R = Me ; R = Ph , whereas P(O-2,4-(t)Bu(2)C(6)H(3))(3) and P(O-2,6-Me(2)C(6)H(3))(3) generate FLPs. Nonetheless, these latter combinations do not react with H(2). The more basic phosphinite tBu(2)POR, R = tBu reacts with B(C(6)F(5))(3) to give (tBu(2)(H)PO)B(C(6)F(5))(3). The related species tBu(2)POR, R = Ph ; 2,6-Me(2)C(6)H(3) showed no reaction with B(C(6)F(5))(3) but the FLPs react under H(2) (4 atm) to give [tBu(2)P(OR)H][HB(C(6)F(5))(3)] R = Ph and 2,6-Me(2)C(6)H(3). Similarly, tBu(2)PCl in combination with B(C(6)F(5))(3), generates an FLP that upon addition of H(2), gives [tBu(2)PH(2)][ClB(C(6)F(5))(3)] albeit in low yield. The diborane 1,4-(C(6)F(5))(2)B(C(6)F(4))B(C(6)F(5))(2) in combination with either tBu(3)P or (C(6)H(2)Me(3))(3)P generates FLPs that react with H(2) to give [R(3)PH](2)[1,4-(C(6)F(5))(2)HB(C(6)F(4))BH(C(6)F(5))(2)] (R = tBu , C(6)H(2)Me(3)). Similarly PhB(C(6)F(5))(2) and tBu(3)P react with H(2) giving [tBu(3)PH][HBPh(C(6)F(5))(2)] . The combination of B(OC(6)F(5))(3) and PtBu(3) also generate an FLP which reacts with H(2) to give [HPtBu(3)][B(OC(6)F(5))(4)] , the product of substituent redistribution. The boronic esters, (C(6)H(4)O(2))BC(6)F(5), (C(6)H(3)FO(2))BC(6)F(5) and (C(6)F(4)O(2))BC(6)F(5), and the borate esters B(OC(6)H(3)(CF(3))(2))(3), B(OC(6)H(2)F(3))(3) and B(OC(6)H(4)CF(3))(3) were prepared and shown to generate FLPs with tBu(3)P or (C(6)H(2)Me(3))(3)P. Nonetheless, no reaction with H(2) was observed for . Collectively these data suggest that there is a threshold of combined Lewis acidity and basicity that is required to effect the splitting of H(2).

Complexation of nitrous oxide by frustrated Lewis pairs.

Frustrated Lewis pairs comprised of a basic yet sterically encumbered phosphine with boron Lewis acids bind nitrous oxide to give intact PNNOB linkages. The synthesis, structure, and bonding of these species are described.