A Ru-η6-arene complex as a C-based Lewis acid in the activation of hydrogen and hydrogenation catalysis.

The PBP ligand (Ph2PC6H4)2BPh was used to prepare ((Ph2PC6H4)2B(Cl)(η(6)-Ph)RuCl (1) and subsequently [((Ph2PC6H4)2B(η(6)-Ph))RuCl][B(C6F5)4] (2). The latter species exhibited Lewis acidity on the η(6)-Ph ring, as reaction with Cy3P gave the donor-acceptor adduct [(Ph2PC6H4)2B(η(5)-C6H5-o-PCy3)RuCl][B(C6F5)4] (3). Steric frustration of this binding was seen with Mes3P, and yet the combination of 2 and Mes3P reacted with H2 to give a 2:1 mixture of 5-o and 5-p, two isomers of [(Ph2PC6H4)2B(η(5)-C6H6)RuCl] (5), along with [Mes3PH][HB(C6F5)3].

Boron azides in Staudinger oxidations and cycloadditions.

Staudinger reactions of Cy2BN3 with tri-substituted phosphines (R3P) yielded the boron-nitrogen-phosphorus linked systems Cy2BN=PR3 (R = Et, (t)Bu, Cy, Ph) (1a-1d respectively). Similarly, reaction of (C6F5)2BN3 with the phosphines P(t)Bu3, PPh3, Ph2PC≡CPh and Ph2PC≡CPPh2 yielded (C6F5)2BN=PR3 (2a-d respectively). In contrast, the reaction of (C6F5)2BN3 with Ph2P-C≡Cp-tol in the presence of excess Me3SiN3 afforded the bicyclic product 3 [1-(C6F5)2B-4-(p-tol)-1H-1,2,3-triazole-5-P(NH)Ph2] in which both a Staudinger and a cycloaddition reaction has taken place.

C-H bond activation by radical ion pairs derived from R3P/Al(C6F5)3 frustrated Lewis pairs and N2O.

Al(C6F5)3/R3P [R = tert-butyl (tBu), mesityl (Mes), naphthyl (Nap)] frustrated Lewis pairs react with N2O to form species having the formula R3P(N2O)Al(C6F5)3, which react with additional alane to generate proposed frustrated radical ion pairs formulated as [R3P·][(μ-O·)(Al(C6F5)3)2] that can activate C-H bonds. For R = tBu, C-H activation of a tBu group affords [tBu2PMe(C(CH2)Me)][(μ-OH)(Al(C6F5)3)2]. In the case of R = Mes, the radical cation salt [Mes3P·][(μ-HO)(Al(C6F5)3)2] is isolated, while for R = Nap, the activation of toluene and bromobenzene gives [(Nap)3PCH2Ph][(μ-OH)(Al(C6F5)3)2] and [(Nap)3PC6H4Br][(μ-HO)(Al(C6F5)3)2], respectively.

Stoichiometric metal-free reduction of CO in syn-gas.

Reaction of a 2:1 mixture of B(C6F5)3 and tBu3P with syn-gas results in the stoichiometric reduction of CO to give a formyl derivative which reacts further via an epoxy-borate intermediate to capture CO, affording a heterocylic alkoxyborate. Heating the reaction prompts reaction with H2 to give a borane-oxy-borate derivative, the product of C-O bond cleavage.

Cycloaddition reactions between dicyclohexylboron azide and alkynes.

The room temperature 1,3-dipolar cycloaddition reactions of the boron azide, Cy2BN3 with the electron-poor acetylenes RCO2C≡CCO2R, EtC≡CCOMe and HC≡CP(=O)Ph2 afforded new 1,2,3-triazoles. In the case of RCO2C≡CCO2R, a new macrocyclic product was isolated with loss of the R group.

CO2 reduction via aluminum complexes of ammonia boranes.

Reactions of amine-boranes NH3BH3, Me2NHBH3, or Me3NBH3 with AlX3 (X = Cl, Br, I, C6F5) have been examined. The species AlBr3·H3BNMe3 2, Al(C6F5)3·H3BNMe3 3, Al(C6F5)3·H3BNHMe2 4 and Al(C6F5)3·H3BNH3 5 have been prepared and isolated. The analogous reaction of B(C6F5)3 and H3BNMe3 results in C6F5-transfer and the formation of (C6F5)BH2·NMe3 6.

Synthesis and reactivity of nickel-hydride amino-bis-phosphinimine complexes.

Cationic hydride complexes [R-N(1,2-CH(2)CH(2)N=PPh(3))(2)NiH][PF(6)] (R = H, Me) are prepared and shown to react with ethylene to produce NiEt complexes and with LiHBEt(3) in bromobenzene to produce NiPh complexes. These species are also thermolysed at 80 °C to orthometallate one of the phenyl groups of the N=PPh(3) substituents.

Activation of CO2 by phosphinoamide hafnium complexes.

Hf-phosphinoamide cation complexes behave as metal-based frustrated Lewis pairs and bind one or two equivalent of CO2 and in as well can activate CO2 in a bimetallic fashion to give a pseudo-tetrahedral P2CO2 fragment linking two Hf centres.

Catalytic reduction of CO(2) to CO by using zinc(II) and in situ generated carbodiphosphoranes.

Playing it 'CO'ol: CO(2) is catalytically reduced to CO with concurrent oxidation of phosphine to phosphineoxide by using an in situ generated catalyst derived from a carbodiphosphorane and zinc(II).

Hydrophosphination of vinyl-boranes with phosphinoamines.

Phosphinoamine ligands PhN(H)PR(2) (R = iPr 1, tBu 2) react with R(1)CH=CR(2)B(C(6)F(5))(2) (R(1) = Ph, p-FC(6)H(4), nPr, Et, R(2) = H, Ph, Et, C(6)F(5)) to effect uncatalyzed hydrophosphination of the olefinic bond, affording the C(2)BNP five-membered cyclization compounds 3-14. All the compounds are fully characterized and compounds 4, 7, 8 and 9 are studied by X-ray diffraction analysis.

Frustrated lewis pair mediated hydrogenations.

The development and use of frustrated Lewis pairs (FLPs) as both stoichiometric and catalytic reductants for the hydrogenation of a variety of organic substrate is described.

The Lewis acidity of fluorophosphonium salts: access to mixed valent phosphorus(III)/(V) species.

Oxidative fluorination of the electron-deficient phosphine Ph(2)P(C(6)F(5)) using XeF(2), followed by fluoride ion abstraction from the resulting difluorophosphorane Ph(2)P(F)(2)(C(6)F(5)), produces electrophilic fluorophosphonium salts [Ph(2)P(F)(C(6)F(5))][X] (X = FB(C(6)F(5))(3) or O(3)SCF(3)). Variable temperature NMR spectroscopic analysis of [Ph(2)P(F)(C(6)F(5))][FB(C(6)F(5))(3)] demonstrates a fluxional process attributed to fluoride ion exchange between B(C(6)F(5))(3) and [Ph(2)P(F)(C(6)F(5))](+), suggesting that these species have comparable Lewis acidities. This exchange can also be illustrated by adding phosphine Ph(3)P to [Ph(2)P(F)(C(6)F(5))][FB(C(6)F(5))(3)] at ambient temperature to produce Ph(2)P(F)(2)(C(6)F(5)) and Ph(3)P-B(C(6)F(5))(3), while heating this mixture results in thermally induced para-substitution of Ph(3)P at the C(6)F(5) group of the phosphonium ion to generate [Ph(3)P(C(6)F(4))P(F)(2)Ph(2)][FB(C(6)F(5))(3)].

Discovery of frustrated lewis pairs: intermolecular FLPs for activation of small molecules.

The discovery of frustrated Lewis pairs is described, as well as the ability of these intermolecular systems to react with a range of small molecules.

Metal-free hydrogenation catalysis of polycyclic aromatic hydrocarbons.

The frustrated Lewis pair, B(C(6)F(5))(3)/Ph(2)PC(6)F(5), acts as an efficient catalyst for the hydrogenation of the polycyclic hydrocarbons including anthracene derivatives, tetracene and tetraphene, at 80 °C and 100 atm H(2) pressure via a mechanism involving protonation of polyaromatic species followed by hydride transfer.

Silyl-migrations in frustrated Lewis pair chemistry: reactions of ((CH3)3Si)3P and B(C6F4H)3 with H2 and CO2.

The 1 : 1 mixture of tris(trimethylsilyl)phosphine and tris(2,3,5,6-tetrafluorophenyl)borane behaves as frustrated Lewis pair (FLP) and shows H(2) and sequential two-step double CO(2) activation with subsequent Me(3)Si group transfer.

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.

Frustrated Lewis pair inspired carbon dioxide reduction by a ruthenium tris(aminophosphine) complex.

Frustrating ruthenium: the ruthenium complex 1 is shown to bind carbon dioxide or aldehyde in a manner similar to a frustrated Lewis pair. Compound 2 catalyzes the reduction of CO(2) in the presence of pinacolborane (HBpin), yielding MeOBpin and O(Bpin)(2) (Ru red, P orange, N green, O light red, C black).

Facile synthesis of electrophilic vinyl boranes: reactions of alkynyl-borates and diazonium salts.

Reactions of alkynylborate salts, easily derived from reaction of frustrated Lewis pairs with terminal alkynes, with diazonium salts to induce 1,1-carboboration affording a facile and efficient route to substituted electrophilic vinyl boranes.

Activation of hydrogen and hydrogenation catalysis by a borenium cation.

The readily prepared borenium salt [(IiPr(2))(BC(8)H(14))][B(C(6)F(5))(4)] (2) [IiPr(2) = C(3)H(2)(NiPr)(2)] is shown to activate H(2) heterolytically in the presence of tBu(3)P. Compound 2 also acts as a catalyst for the metal-free hydrogenation of imines and enamines at room temperature.

Rearrangements of phosphinoimines to phosphine-imines in ruthenium chelate complexes.

Thermal reaction of 1:1 mixtures of the RuCl(2)(PPh(3))(3) and phosphinoimine R(2)PN=CPh(2) (R = Ph, iPr, Me) at 140 °C results in isolation of the dimeric species [RuCl(μ-Cl)(PPh(3))(C(6)H(4)(PPh(2))C(Ph)NH)](2) (R = Ph 1, iPr 2, Me 3) containing phosphine-imine chelating ligands. Subsequent reaction of 1 and 3 with one equivalent of pyridine at room temperature give RuCl(2)(PPh(3))(py)(C(6)H(4)(PR(2))C(Ph)NH) (R = Ph 4, Me 5). Excess pyridine reacts with 2 to give a mixture of the cis and trans-isomers of RuCl(2)(py)(2)(C(6)H(4)(PiPr(2))C(Ph)NH) 6 and 7 respectively.