Verkade Base in FLP Chemistry–From Stoichiometric C–H Bond Cleavage to the Catalytic Dimerization of Alkynes

Abstract

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.

Small Molecule Activation with Intramolecular “Inverse” Frustrated Lewis Pairs

“…Instead, classical Lewis acid-base adducts were isolated with no evidence of NÀHb ond activation via hydrogen bonding between coordinated NH 3 and the Lewis basic phosphine center. To gain more information, FLP 5 was treated with NH 3 (pK a = 41 in DMSO), [17] benzyl amine andp yrrolidine (pK a = 44 in DMSO), [17] respectively,i nC 6 D 6 as solvent and the outcomeo ft hese reactions was monitored by 1 H, 13 Ca nd 11 BNMR spectroscopy.T he solution NMR data revealed quantitative formation of the Lewis acid base adducts 19-21. In all cases, up-fields hifts of the boron signals in the 11 BNMR spectra from 80.6 ppm for the trigonal planar boron of 5 to À6.7 (19), À4.7 (20)a nd À3.1 (21)ppm of the amine adducts were noted, clearly suggesting N!Bc oordination. Gratifyingly,N H 3 adduct 19 could be isolated in 87 %y ield as a stable crystalline material and structurally fully characterized.…”

“…The structural parameters of 15 are very similar to those of 13 and 14 (Figure 4). Although terminal alkyne activation is common in FLP chemistry and the FLP catalyzed dimerization of terminala lkynest ogem-1,3-enynes has recently been disclosed, [19] the FLP mediated deprotonation of HCCH has not yet been reported nor have any catalytic transformation been documented. Given the easeb yw hich alkynes can be activated with our most potent FLP 5,w ew ondered whether other simple organic molecules with similar CÀHa cidities would also undergo FLP mediated deprotonation reactions (Scheme 6).…”

“…SelectedC ÀNa nd BÀCd istances[pm] of 3, 5,[13][14][15][18][19][20]. Note also that this is different from guanidinium borate 18 showing N1ÀH1•••O1 hydrogen bond interactions [N1•••O1,2 59 pm],b ut with H1 covalently bound to guanidinium nitrogen N1.…”

Selective Manganese-Catalyzed Dimerization and Cross-Coupling of Terminal Alkynes

“…Cl Cl (Z)-4,4'-(but-1-en-3-yne-1,4-diyl)bis(chlorobenzene) 5 (6), purified by column chromatography (15g SiO2, PE/Et2O 1:1) slightly yellow solid, 99 mg (92%). 1 2, 136.6, 136.1, 135.6, 134.3, 131.6, 130.4, 130.1, 123.3, 109.2, 96.7, 90.3 ppm.…”

“…This process is accompanied by H-H and metal-σ-C bond cleavage and is typically the final step in both stoichiometric and catalytic hydroformylations of alkenes (Scheme 1). 5,6 Scheme 1. Formation of a Mn(I) Hydride and Acetylide Species via Alkyl Migration followed by Aldehyde Release upon E-H Bond Cleavage We have recently described the hydrogenation of alkenes and nitriles utilizing Mn(I) complexes fac-[Mn(dpre)(CO)3(R)] (dpre = 1,2-bis(di-n-propylphosphino) ethane, R = CH3, CH2CH3, CH2CH2CH3) and fac-[Mn(dippe)(CO)3(CH2CH2CH3) (dippe = 1,2-bis(di-iso-propylphosphino)ethane) where we took advantage of the migratory insertion and hydrogenolysis processes to create the active 16e -Mn(I) hydride catalysts (Scheme 1).…”