Reactions of a Bis(pentalene)dititanium complex with alkenes; the molecular structure of the butadiene complex [Ti2(µ: η5, η5-Pn††)2(μ: η2, η2-s-trans-C4H6)] (Pn†† = 1, 4-(SiiPr3)2-C8H4). (15th January 2022)

• Record Type: Journal Article
• Authors: Molloy, Matthew; Kilpatrick, Alexander F.R.; Tsoureas, Nikolaos; Cloke, F. Geoffrey N.
• Is Part Of: Polyhedron. Volume 212(2022)
• Publication Date: 2022-01-15
• Subjects: Titanium -- Alkene complex -- Pentalene. bi-metallic -- Agostic; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2021.115574
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: Reaction of the syn -bimetallic complex (1 ) with 1, 3-butadiene results in the formation of (2 ), featuring an essentially planar butadiene ligand. Reaction of (1 ) with propene affords the "tuck-over" alkene π-complex (3 ) with concurrent loss of propane; kinetic studies suggest involvement of a Ti-H(iPr) agostic interaction in the latter reaction. Abstract: Reaction of the syn -bimetallic complex [Ti2 (µ:η 5, η 5 -Pn †† )2 ] (1 ) (Pn †† = 1, 4-(Si i Pr3 )2 -C8 H4 ) with 1, 3- trans -butadiene in toluene results in the clean formation of the 1:1 adduct [Ti2 (µ:η 5, η 5 -Pn †† )2 (μ: η 2, η 2 -s- trans -C4 H6 )] (2 ) featuring an essentially planar butadiene ligand. Complex (2 ) represents the first example of a bimetallic early transition metal complex where a coordinated butadiene adopts such a conformation. When (1 ) is reacted with propene an unexpected "tuck-over" alkene π-complex (3 ) is formed with co-current loss of propane. Complex (3 ) features a coordinated η 2, η 1 vinylic (H2 C = CMe)-Si i Pr2 -Pn † moiety as a result of CH activation of one of the isopropyl substituents of the Si i Pr3 groups on the Pn †† supporting ligand. One of the hydrogens of this secondary vinylic moiety is significantly shifted upfield in the 1 H NMR spectrum of (3 ) and a single crystal XRD study shows an interaction between this hydrogen and one of the Ti centres. Preliminary kinetic studies of the formation of (3 ) show a slightly negative entropy of activation and 1st order consumption of (1 ) both of which suggest the involvement of a Ti-H( i Pr) agostic interaction during the cyclometallation reaction.