A new approach to intermolecular frustrated Lewis pairs (FLPs) that combines readily available bulky organosuperbases with moderate to weak boron-containing Lewis acids is reported. These so-called "inverse" FLPs are demonstrated to heterolytically cleave dihydrogen, allowing for the isolation and structural characterization of various phosphonium borohydride salts; two FLPs proved to be efficient catalyst's in the metal-free hydrogenation of N-benzylidenaniline.

For the first time have boron-containing weak Lewis acids been demonstrated to be active components of Frustrated Lewis Pair (FLP) catalysts in the hydrogenation of ketones to alcohols. Combining the organosuperbase (pyrr) P=NtBu with the Lewis acid 9-(4-CF -C H )-BBN generated an "inverse" FLP catalyst capable of hydrogenating a range of aliphatic and aromatic ketones including N-, O- and S-functionalized substrates and bio-mass derived ethyl levulinate. Initial computational and experimental studies indicate the mechanism of catalytic hydrogenation with "inverse" FLPs to be different from conventional FLP catalysts that contain strong Lewis acids such as B(C F ) .

A series of mono- and binuclear Lewis acid-base complexes of the formulas N[CHCHN(Pr)]P→LA [LA = BH (8), Ga(CF) (10), GaCl (11)], LA←N[CHCHN(Pr)]P [LA = Al(CF) (6a), AlMe (6b), AlEt (6c), AlBu (6d), BF (13)], and LA←N[CHCHN(Pr)]P→LA [Lewis acid (LA) = Al(CF) (7a), AlMe (7b), AlEt (7c), AlBu (7d), AlCl (7e), BH (9)] were generated from reactions of Verkade's base, N[CHCHN(Pr)]P (1), with various boron-, aluminum-, and gallium-containing Lewis acids, and characterized by multinuclear NMR spectroscopy. {N[CHCHN(Pr)]P→CH}[BF] (5) was synthesized via the treatment of 1 with [CH][BF]. The reaction of 1 with B(CF), followed by the addition of [PhC][BCl], gave rise to the rearranged borate salt [PNCH(Pr)][BCl] (3), while treating 1 with [PhC][BCl] exclusively afforded {N[CHCHN(Pr)]PH}[BCl] (4). Reactions of 1 with 2 equiv of GaCl and BF, respectively, afforded the novel phosphenium gallate and borate salts 12a, 12b, and 15. The solid-state structures of 1, 3-5, 6b, 7a, 7b, 7e, 8, 10, 11, 12b, 13, and 15 were determined by X-ray crystallography.

Stoichiometric and catalytic reactions of terminal alkynes with various FLPs and Lewis acid–base adducts have been investigated. Reactions of phenylacetylene with FLPs composed of the Verkade base N­[CH2CH2NPri]3P (1) and the Lewis acids BPh3, 9-hexyl-BBN, and 9-BBN gave [N­(CH2CH2NPri)3PH]­[PhCC-BPh3] (2), [N­(CH2CH2NPri)3PH]­[9-hexyl-9-PhCC-BBN] (3), and [N­(CH2CH2NPri)3PH]­[9-PhCHCH-9-PhCC-BBN] (4). The binuclear Lewis acid–base adduct (C6F5)3Al–N­[CH2CH2NPri]3P–Al­(C6F5)3 (6) effectively catalyzed the dimerization of terminal alkynes to gem-1,3-enynes.

Synthesis and structure of sterically overloaded tetra-coordinated yttrium and lanthanum disiloxides, Inorganic Chemistry Communications (2016Communications ( ), doi: 10.1016Communications ( /j.inoche.2016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT Synthesis and Structure of Sterically Overloaded Tetra-coordinated Yttrium and Lanthanum DisiloxidesBrian McNerney [a] , Suresh Mummadi [a] , Fernando Hung-Low [a] , David B. Cordes [b] , Daniel K.Unruh [a] , Clemens Krempner* [a] [a] Department of Chemistry & Biochemistry, Texas Tech University, Box 1061, Lubbock, Texas, 79409-1061 In the past half century, rare earth metal siloxides [1] have gained some popularity primarily due to their potential as homogeneous catalysts in polymerization catalysis [2][3][4] , as precursors for the formation of metal oxides and silicates [5][6][7] , and as models for silica-supported lanthanide metal heterogeneous catalysts. [8][9][10][11][12][13] In particular work by the Edelmann group has resulted in significant advancements in the synthesis of rare earth metal complexes supported by the. [12][13][14][15][16][17][18][19][20] Our group recently synthesized a sterically overloaded silanediol of formula (CH 2 SiR 2 OH) 2 (1),where R = Si(SiMe 3 ) 2 Me, and demonstrated that its deprotonated form serves as a dianionic chelating spectator ligand for aluminum alkyls, hydroxides and alkoxides. [21] One of these complexes, a monomeric aluminum isopropoxide (Scheme 1) proved to be one of the most active MPV A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTcatalyst for the reduction of ketones and aldehydes reported so far. [22] Key to its high activty was its monomeric nature enforced by the bulkiness of the supporting disiloxide ligand. Based on these results, we reasoned that sterically overloaded disilanol 1 might be the ideal ligand for the synthesis of heteroleptic and salt-and adduct-free rare earth siloxide complexes, the latter potentially useful as Lewis acid catalysts.Scheme 1. Synthesis of sterically overloaded aluminum disiloxides.We first attempted to prepare the heteroleptic yttrium and lanthanum disiloxides of formula [(CH 2 R 2 SiO) 2 MN(SiMe 3 ) 2 ] (M = Ln, Y; R = SiMe(SiMe 3 ) 2 ) (2), respectively, as illustrated in Scheme 2. Initially, one equivalent of disilanol 1 was reacted with one equivalent of La(N(SiMe 3 ) 2 ) 3 in toluene as solvent. The reaction, however, did not give 2 but instead yielded the spirocyclic lanthanum disiloxide 3 as the main product irrespective whether toluene, THF or hexanes were used as solvents. Best yield...