Different coordination modes of an aryl-substituted hydrotris(pyrazolyl)borate ligand in rhodium and iridium complexes

Complexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared by reaction of KTptol with the appropriate [RhCl(olefin)2]2 dimer (Tptol means hydrotris(3-p-tolylpyrazol-1-yl)borate). The two complexes show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N’,N’’,C-Tptol)Ir(Ph)(N2) (3) by irradiation with UV light under a dinitrogen atmosphere. Compound 3 constitutes a rare example of Ir(III)–N2 complex structurally characterized by X-ray crystallography. Its N2 ligand can be easily substituted by acetonitrile or ethylene upon heating and denticity changes in the Tptol ligand, from κ4-N,N’,N’’,C (monometallated Tptol, from now on represented as Tptol′) to κ5-N,N′,N″,C,C″ (dimetallated Tptol ligand, represented as Tptol″) have been observed. When complex 3 is heated in the presence of acetylene, dimerization of the alkyne takes place to yield the enyne complex [(κ5-N,N′,N′′,C,C′-Tptol)Ir(CH2CHCCH), 7¸ in which the unsaturated organic moiety is bonded to iridium through the carbon–carbon double bond.

Graphical abstractComplexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared and found to show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N’,N’’,C-Tptol)Ir(Ph)(N2) (3).Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Rhodium-diene complexes containing the Tptol ligand have been prepared. ► The new complexes show dynamic behavior between κ2 and κ3 coordination modes of the ligand. ► Analogous iridium complexes have been synthesized. ► An unusual Ir-N2 compound has been isolated and structurally characterized. ► Dimerization of acetylene to an enyne by the Ir-N2 complex has been achieved.