Carbon–Nitrogen Bond Construction and Carbon–Oxygen Double Bond Cleavage on a Molecular Titanium Oxonitride: A Combined Experimental and Computational Study

Abstract

New carbon-nitrogen bonds were formed on addition of isocyanide and ketone reagents to the oxonitride species [{Ti(η(5)-C5Me5)(μ-O)}3(μ3-N)] (1). Reaction of 1 with XylNC (Xyl = 2,6-Me2C6H3) in a 1:3 molar ratio at room temperature leads to compound [{Ti(η(5)-C5Me5)(μ-O)}3(μ-XylNCCNXyl)(NCNXyl)] (2), after the addition of the nitrido group to one coordinated isocyanide and the carbon-carbon coupling of the other two isocyanide molecules have taken place. Thermolysis of 2 gives [{Ti(η(5)-C5Me5)(μ-O)}3(XylNCNXyl)(CN)] (3) where the heterocumulene [XylNCCNXyl] moiety and the carbodiimido [NCNXyl] fragment in 2 have undergone net transformations. Similarly, tert-butyl isocyanide (tBuNC) reacts with the starting material 1 under mild conditions to give the paramagnetic derivative [{Ti3(η(5)-C5Me5)3(μ-O)3(NCNtBu)}2(μ-CN)2] (4). However, compound 1 provides the oxo ketimide derivatives [{Ti3(η(5)-C5Me5)3(μ-O)4}(NCRPh)] [R = Ph (5), p-Me(C6H4) (6), o-Me(C6H4) (7)] upon reaction with benzophenone, p-methylbenzophenone, and o-methylbenzophenone, respectively. In these reactions, the carbon-oxygen double bond is completely ruptured, leading to the formation of a carbon-nitrogen and two metal-oxygen bonds. The molecular structures of complexes 2-4, 6, and 7 were determined by single-crystal X-ray diffraction analyses. Density functional theory calculations were performed on the incorporation of isocyanides and ketones to the model complex [{Ti(η(5)-C5H5)(μ-O)}3(μ3-N)] (1H). The mechanism involves the coordination of the substrates to one of the titanium metal centers, followed by an isomerization to place those substrates cis with respect to the apical nitrogen of 1H, where carbon-nitrogen bond formation occurs with a low-energy barrier. In the case of aryl isocyanides, the resulting complex incorporates additional isocyanide molecules leading to a carbon-carbon coupling. With ketones, the high oxophilicity of titanium promotes the unusual total cleavage of the carbon-oxygen double bond.

Structural Diversity in the Reactions of Dimetallic Alkyl Titanium Oxides with Isonitriles and Nitriles

“…It is noteworthy that the incorporation of the organic nitrile opens the Ti–O–Ti angle (180.0°) with respect to the precursor complex 1 (153.4(1)°) . Structural parameters related to the ketimido fragment, Ti1–N1 1.865(2) Å, N1–C31 1.257(3) Å, and Ti1–N1–C31 167.5(2)°, are similar to those of other titanium­(IV)–ketimido complexes. − …”

Azavinylidene Complexes from Coupling Reactions of Organonitriles with Phosphines

“…The azavinylidene complex ReCl 3 (PMePh 2 ) 2 {NC­(PMePh 2 )­Me} ( 8a ) is interesting as it represents the first example of an azavinylidene complex with a phosphine (PR 3 ) substituent. Reported azavinylidene complexes are mainly confined to those with H, alkyl, and aryl substituents. , A few rhenium azavinylidene complexes have been reported and were generated by alternative routes, , for example, protonation of nitrile complexes, , deprotonation of imido complexes , and insertion of nitriles …”

Cp2Ti(κ2-tBuNCNtBu): A Complex with an Unusual κ2 Coordination Mode of a Heterocumulene Featuring a Free Carbene

“…33 Only two other examples of Ti 2 (μ-C(NR) 2 ) complexes have been structurally characterized, both of which are within structured Ti III /Ti III bimetallic motifs with a μ-η 2 ,η 2 -C(NR) 2 bonding pattern. 100,101 Both complexes demonstrated similar extents of activation of the carbodiimide moiety in the solid state as observed in 10, but have shorter Ti−C distances (approximately 2.1 Å); however, due to the rigid bimetallic frameworks, direct structural comparison between these structures is difficult.…”