Catalytic PH Activation by Ti and Zr Catalysts

Abstract

Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*2Zr(mu-H)3Li]3 (1 a) or [Cp*2Zr(mu-H)3K(thf)4] (1 b), and the metallocycles [CpTi(NPtBu3)(CH2)4] (6) and [Cp*M(NPtBu3)(CH2)4] (M=Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R=Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)n (n=4, 5) while reaction of tBu3C6H2PH2 gave the phosphaindoline tBu2(Me2CCH2)C6H2PH 9. Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp*2Zr((PR)2)H][K(thf)4] (R=Ph 2, Cy 3, C6H2Me3 4), [Cp*2Zr((PPh)3)H][K(thf)4] (5), [CpTi(NPtBu3)(PPh)3] (7) and [CpTi(NPtBu3)(mu-PHPh)]2 (8), while reaction of 6 with (C6H2tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe3)(P(C6H2tBu3)] (10). The secondary phosphines Ph2PH and (PhHPCH2)2CH2 also undergo dehydrocoupling affording (Ph2P)2 and (PhPCH2)2CH2. The bisphosphines (CH2PH2)2 and C6H4(PH2)2 are dehydrocoupled to give (PCH2CH2PH)2)(12) and (C6H4P(PH))2 (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)2 (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))2 (18) and subsequently [(Me2C6H2P2)2(mu-Me2C6H2P2)]2 (19). Stoichiometric reactions with these bisphosphines gave [Cp*2Zr(H)(PH)2C6-H4][Li(thf)4] (22), [CpTi(NPtBu3)(PH)2C6H4]2 (23) and [Cp*Ti(NPtBu3)(PH)2C6H4] (24). Mechanistic implications are discussed.

Nucleophilic Phosphinidene Complexes: Access and Applicability

“…For example, compound 26 undergoes reductive elimination and reacts with one equivalent of the primary phosphine Mes*PH 2 in the presence of a threefold excess of PMe 3 to afford the isolable 27 (Scheme 9). [32] Although the structure of 27 could not be confirmed crystallographically, its resonances at d = 769.9, 35.3, and À10.3 ppm in the 31 P NMR spectrum are indicative of the terminal titanium phosphinidene fragment, the phosphinimide ligand, and the coordinated PMe 3 , respectively. Additional 1 H and 13 C{ 1 H} NMR spectra were consistent with this formulation.…”

Dehydrogenative Bond-Forming Catalysis Involving Phosphines: Updated Through 2010

“…Since their initial report, Stephan and coworkers have developed a family of neutral titanium and zirconium catalysts CpTi(NP t Bu 3 )(CH 2 ) 4 (5) and Cp*M(NP t Bu 3 )(CH 2 ) 4 (6, M = Ti; 7, M = Zr) [26]. For example, reaction of PhPH 2 with 1 mol% 5 gave (PPh) 5 in 41% yield (eq.…”

“…The use of a phosphinimide ligand to support the metal is based on the hypothesis that these ligands provide a monoanionic charge and steric bulk slightly remote from the metal which is complementary to cyclopentadienyl-derived ligands [27]. These phosphinimide complexes, however, appear to dehydrocouple primary phosphines at a qualitatively slower rates than the anionic zirconocene hydride derivatives [26].…”

Group 2 Mediated Dehydrocoupling

“…164,171 In these cases oligomerisation of primary phosphines yielded a variety of (RP) n compounds, with n showing a marked dependence on the nature, most notably the steric demands, of R; substituted phenyl substituents tend towards n = 5 while the more demanding naphthyl derivatives yield tetramers. 172,173 The precatalysts in each of these reactions were possessed of at least 2 reactive ligand fragments and analysis of the This mechanism is reminiscent of FLP chemistry, with the highly electrophilic phosphorus centre interacting with the silane Si-H bond to render the silane amenable to nucleophilic attack. This step yields an ammonium cation in the presence of an acidic P(V)-H bond, the interaction of which yields the product silylamine, dihydrogen and reforms the electrophilic phosphonium cation upon which the reactivity is contingent.…”