NO₂bond cleavage by MoL₃complexes

Abstract

The cleavage of one N-O bond in NO2 by two equivalents of Mo(NRAr)3 has been shown to occur to form molybdenum oxide and nitrosyl complexes. The mechanism and electronic rearrangement of this reaction was investigated using density functional theory, using both a model Mo(NH2)3 system and the full [N((t)Bu)(3,5-dimethylphenyl)] experimental ligand. For the model ligand, several possible modes of coordination for the resulting complex were observed, along with isomerisation and bond breaking pathways. The lowest barrier for direct bond cleavage was found to be via the singlet η(2)-N,O complex (7 kJ mol(-1)). Formation of a bimetallic species was also possible, giving an overall decrease in energy and a lower barrier for reaction (3 kJ mol(-1)). Results for the full ligand showed similar trends in energies for both isomerisation between the different isomers, and for the mononuclear bond cleavage. The lowest calculated barrier for cleavage was only 21 kJ mol(-1)via the triplet η(1)-O isomer, with a strong thermodynamic driving force to the final products of the doublet metal oxide and a molecule of NO. Formation of the full ligand dinuclear complex was not accompanied by an equivalent decrease in energy seen with the model ligand. Direct bond cleavage via an η(1)-O complex is thus the likely mechanism for the experimental reaction that occurs at ambient temperature and pressure. Unlike the other known reactions between MoL3 complexes and small molecules, the second equivalent of the metal does not appear to be necessary, but instead irreversibly binds to the released nitric oxide.

Sulfur Dioxide Activation: A Theoretical Investigation into Dual S═O Bond Cleavage by Three-Coordinate Molybdenum(III) Complexes

“…The N[ t Bu]Ph ligand is more relevant to the experimental ligand (eq ). The quartet Mo(NH 2 ) 3 (1_Q) is lower in energy than its doublet (1_D) by 58.2 kJ/mol, which is in accordance with earlier studies. ,,,− Consequently, the reaction pathway will begin along the quartet surface, as the ground state for SO 2 is a singlet. The earlier studies have revealed that there are two different conceivable approaches for bond cleavage within small molecules: mononuclear and binuclear mechanisms.…”

“…The nomenclature used in this paper is as follows: (i) N (numbers) represent minima and TS represent intraconversion transition structures; (ii) spin-states are denoted by S (singlet), D (doublet), T (triplet), Q (quartet), and Q T (quintet); (iii) breaking transition structures by TSB ; (iv) the N[ t Bu]Ph ligand is represented by the Ar script; and (v) the N[ t Bu]Ph ligands are oriented in an almost C 3 V , propeller-like arrangement, which has been reported as the most likely low-energy conformation …”

“…Cummins et al have reported the ability of Mo(N[R]Ar) 3 (R = C(CD 3 ) 2 CH 3 , Ar = 3,5-C 6 H 3 Me 2 ) to cleave bonds within various small molecules, − including both tri- and tetra-atomic species. , These experimental results on Mo(N[R]Ar) 3 have also been complemented by several theoretical studies in the literature. − Of significant importance is the reactivity of Mo(N[R]Ar) 3 toward a SO 2 molecule (eq ). Initially, 1 equiv of Mo(N[R]Ar) 3 was reacted with SO 2 , which produced the Mo-oxo complex, (N[R]Ar) 3 Mo(O) (confirmed by 2 H-NMR spectroscopy).…”

Reactions of the Unsaturated Ditungsten Complexes [W2Cp2(μ-PPh2)2(CO)x] (x = 1, 2) with Nitric Oxide: Stereoselective Carbonyl Displacement and Oxygen-Transfer Reactions of a Nitrite Ligand

“…2.189(11) Å in (PPh 4 )[W( N -NO 2 )­(CO) 5 ]) . Similar energetic differences have been recently computed for nitrito and nitro isomers of [MoL 3 (NO 2 )] complexes (L 3 = triamide ligands), also revealing low kinetic barriers for the conversion between the different linkage isomers of the nitrite ligand …”

“…26 Similar energetic differences have been recently computed for nitrito and nitro isomers of [MoL 3 (NO 2 )] complexes (L 3 = triamide ligands), also revealing low kinetic barriers for the conversion between the different linkage isomers of the nitrite ligand. 27 Stereoselectivity in the Reactions of 1 and 2 with NO. We have investigated the selective formation of either cis or trans dinitrosyl complexes with the help of DFT calculations on some of the critical steps (see the Experimental Section and Supporting Information).…”