Allyl Palladium Complexes of Cycloheptatrienyl‐Cyclopentadienyl Phosphane Ligands in Buchwald‐Hartwig Amination Reactions

Abstract

A series of well-defined palladium allyl chloride precatalysts was synthesized using previously reported troticenyl phosphane ligands [(η 7 -C 7 H 7 )Ti(η 5 -C 5 H 4 PR 2 )] and [(η 7 -C 7 H 6 PR 2 )Ti(η 5 -C 5 H 5 )] (R = Cy, tBu) as ancillary ligands. The formation of a dimeric μ-chloro-, μ-allyl-bridged Pd I species was observed with the ligand [(η 7 -C 7 H 7 )Ti(η 5 -C 5 H 4 PtBu 2 )], whereas L 2 Pd 0 {L = [(η 7 -C 7 H 6 PtBu 2 )Ti(η 5 -C 5 H 5 )]} was formed in presence of KOtPent. In addition, the catalytic activity of the palladium [a] 2569 Scheme 1. Troticenyl phosphane ligands (top) and Pd 0 complexes with ligand 4 tBu and 5 tBu (bottom). 2570 Figure 4. ORTEP diagrams of 7 tBu 1Me, 7 tBu 2Me, and 7 tBu 1Ph (solvent omitted) with thermal displacement ellipsoids drawn at 50 % probability. Hydrogen atoms are omitted for clarity.

Transition-Metal Complexes of Diphosphanes Containing the η7-Cycloheptatrienyl-η5-Cyclopentadienyl Titanium (Troticene) Sandwich Moiety

“…Unfortunately, all attempts to establish complexes with an intramolecular Ti–Pd or Ti–Pt bond by chloride abstraction have been unsuccessful to date, while the isolation of the titanium­(IV)–platinum(0) complex 10 provides further evidence for the ability of the Cht-Cp titanium (troticene) unit to act as an integrated reducing agent. This reactivity had previously been exploited for the application of troticene-based monophosphanes in palladium-catalyzed cross-coupling reactions, − and accordingly, this aspect has to be considered for future applications of the novel troticene-based diphosphanes in homogeneous catalysis.…”

“…For η 7 -cycloheptatrienyl-η 5 -cyclopentadienyl titanium (troticene, 1 ), similar synthetic methods for the preparation of functionalized phosphanes were reported. − Selective functionalization either at the five- or seven-membered ring or at both rings can be realized; , a series of phosphanes of the types 2 R (R = Ph, i Pr, Cy, t Bu) and 3 R (Ph, Cy, t Bu) were prepared, and their reactivity was investigated by forming several heterobimetallic complexes with transition metals. − In the case of Pd­(OAc) 2 , reduction of palladium and formation of L 2 Pd 0 complexes was observed. Recently, the monophosphanes 2 R and 3 R have been employed as ligands in cross-coupling reactions, revealing a major influence of the phosphane (PR 2 ) moiety on the catalytic reactions. − In contrast, the reactivity of 1,1′-bis­(phosphanyl)­troticenes 4 R has scarcely been investigated; a series of heterobimetallic complexes of molybdenum, chromium, cobalt, manganese, and iron were isolated, which contain 1,1′-bis­(diphenylphosphanyl)­troticene (dppti, 4 Ph ). , The methyl analogue 4 Me was also prepared and employed for the preparation of chromium, molybdenum, iron, and nickel complexes, in which the diphosphane acts as a chelating or bridging ligand . These early examples of 1,1′-bis­(phosphanyl)­troticene complexes were complemented more recently by the platinum dichloride complex 5 (Figure ).…”