4d vs. 5d – Reactivity and Fate of Terminal Nitrido Complexes of Rhodium and Iridium

Abstract

The stability of (pyridinediimine)rhodium– and ‐iridium–azido complexes was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and DFT calculations. On a preparative scale, the isolation and X‐ray crystallographic characterization of the thermolysis products confirmed intramolecular C–H activation processes with concomitant reorganisation of C–C, C–N, N–H and Ir–N bonds to yield tuck‐in complexes with a different constitution of the ligand framework for the Rh and Ir products. The tentatively formed (Rh) or initially present (Ir) nitrido unit was converted into either an amine (Rh) or amido (Ir) moiety. Furthermore, the dimerization of the nitrido complexes to the corresponding dinitrogen compounds, i.e. 2 LnM≡N → LnM–N2–MLn, was investigated. Experimental evidence for the relevance of this step was provided by the isolation and X‐ray crystallographic characterization of a related dinuclear N2‐bridged (pyridinediimine)dirhodium complex. DFT calculations revealed that the formation of dinitrogen complexes is thermodynamically strongly favourable and evidenced that the previous isolation of a terminal iridium–nitrido complex was possible due to a high barrier for the dimerization process and a sizeable barrier for the intramolecular C–H activation step.

Formation and Reactivity of the Terminal Vanadium Nitride Functionality

“…Treatment of 1 with 10 mol-% of [(nacnac)V(Ntol 2 )] in hexanes at room temperature produced immediate gas evolution and, over a period of 2 h, resulted in the formation of a yellow-brown solution concurrent with the precipitation of 3 as a yellow solid in 74 % isolated yield (Scheme 9). The unambiguous formation of 3 was confirmed by multinuclear ( 1 H, 13 C, 51 V) NMR and IR vibrational spectroscopy. Likewise, the reaction of 2 and 10 mol-% of [(nacnac)V(Ntol 2 )] immediately yielded nitride product 4 in 70 % isolated yield after 3 h (Scheme 9).…”

“…After stirring for 0.5 h, all volatiles were removed under reduced pressure. Characterization of the product by multinuclear ( 1 H, 13 C, 19 F) NMR spectroscopy (C 6 D 6 , 25°C) revealed a diamagnetic nitride-borate vanadium complex, which has been independently observed after…”

“…A few exemplary and unique reactions mediated by metal nitrides include direct insertion into C-H bonds, [12-14a] bioinspired hydrogenation to form the parent metal amide and ammonia, [6,15,16] complete and incomplete N-atom transfer to form C-N bonds from π-acids (CO, CNR), [16][17][18][19][20] and multi-electron reductive coupling reactions to render metal-dinitrogen complexes. [13,21] Moreover, a new and synthetically important application of molybdenum nitrides is the generation of molybdenum alkylidyne catalysts for alkyne metathesis geared towards the formation of carbon-carbon triple bonds for the synthesis of polymers and other organic commodity reagents. [22][23][24][25][26] Perhaps the most efficient and atom-economical route to the metal nitride functionality is that of the activation and cleavage of atmospheric dinitrogen [Reaction (1), Scheme 1], as witnessed in the landmark chemistry of threecoordinate [(tBuArN) 3 Mo] (Ar = 3,5-Me 2 C 6 H 3 ).…”

“…Therefore, we have been unable to measure rates with certainty. As reported earlier, complex 4 has been fully characterized by multinuclear NMR ( 1 H, 13 C, and 51 V) and IR vibrational spectroscopy. [54,55] …”

Homo- and Heterobimetallic Complexes in Catalysis

“…Indeed, when Ru 2 [d(3,5Cl 2 )Phf]N 3 (104) is heated under vacuum in the solid state, N 2 is lost but the corresponding nitride complex could not be identified. Several mononuclear nitride complexes are reported to insert N atom into alkyl C-H bond via radical-type reactions [259][260][261][262][263]. This reaction also proceeds photolytically.…”