A Kinetic Study of the Ring-Opening Process in Tungsten Carbonyl Complexes Containing Hemilabile Metallodithiolate Ligands

Abstract

The synthesis of the metallodithiolate derivative of tungsten pentacarbonyl from the reaction of photogenerated W(CO)(5)THF and Ni-1 ((1,5-bis(2-mercapto-2-methylpropane)-1,5-diazacyclooctanato)nickel(II)) is described, along with its crystal structure. In N,N-dimethylformamide solution, the pentacarbonyl exists in equilibrium with its tetracarbonyl analogue and carbon monoxide. The pentacarbonyl complex stereoselectively loses cis carbonyl ligands, as is apparent from (13)CO-labeling studies, where the thus-formed tetracarbonyl tungsten complex resulting from chelate ring-closure is preferentially (13)CO-labeled among the two mutually trans CO groups. The kinetics of the addition of CO to the tetracarbonyl to afford the metal pentacarbonyl were monitored by means of in situ infrared spectroscopy in the nu(CO) region at CO pressures between 28 and 97 bar and temperatures over the range 45-60 degrees C. Under these conditions, there was no evidence for W-S bond cleavage in the pentacarbonyl complex with concomitant formation of W(CO)(6). These studies reveal that the tetracarbonyl complex and CO are only slightly unstable with respect to the formation of the pentacarbonyl complex, with an equilibrium constant at 50 degrees C of about 2.8 M(-1) or DeltaG degrees = -1.4 kJ/mol. The activation parameters determined for the ring-opening process (DeltaH = 89.1 kJ/mol and DeltaS = -37.2 J/mol.K) suggest a solvent-assisted concerted ring-opening mechanism.

cis-Dithiolatonickel as metalloligand to dinitrosyl iron units: the di-metallic structure of Ni(μ-SR)[Fe(NO)2] and an unexpected, abbreviated metalloadamantyl cluster, Ni2(μ-SR)4[Fe(NO)2]3

“…21 As indicated in eqn (1), sparges of CO gas did not return complex 1 to the starting materials under ambient conditions (1 atm, 22 • C). This result is consistent with the strong binding of the nickeldithiolate ligand to W 0 (CO) 5 and Fe 0 (CO) 4 , demonstrated by a similar non-productive, or very slow, reaction with CO. 3,14, 19 Nevertheless, and similar to observations for (c), in the presence of 13 C-labeled CO, exchange occurs into complex 1 dissolved in THF solvent. This labeled material was useful for 13 C NMR spectra, showing a singlet at 210.07 ppm, illustrative of the diamagnetism of the complex (Fig.…”

“…Within the Ni(N 2 S 2 ) metalloligand there are no significant metric differences between bound and free forms, as has been noted in other structures in which it serves as a monodentate ligand. 16, 19 Likewise, the S-bound pendant iron nitrosyl group has bond distances and angles consonant with other LFe(NO) 2 (CO) structures, L = NHC (IMes) or PPh 3 , 13,20 in which the iron unit is in the diamagnetic, reduced form, {Fe(NO) 2 } 10 (Enemark-Feltham notation), as it is in 1. 21 As indicated in eqn (1), sparges of CO gas did not return complex 1 to the starting materials under ambient conditions (1 atm, 22 • C).…”

New dinuclear nickel(ii) and iron(ii) complexes with a macrocyclic ligand containing a N6S2 donor-set: Synthesis, structural, MALDI-TOF-MS, magnetic and spectroscopic studies

“…This result suggests that two counterions are uncoordinated in solution. 29 The molar conductance values for the halidecomplexes, in acetone, lie in the range reported as 1 : 1 electrolytes, for compounds (7) and (8), and between the range reported as 2 : 1-3 : 1 electrolytes, for compounds ( 9) and (10).…”

“…were isolated from the reaction between the complex [Ni 2 L](BF 4 ) 4 •7H 2 O (3) and the corresponding tetrabutylammonium halide. The fluoride (7), chloride (8) and bromide (9) complexes show a blue colour, while the iodide (10) complex was green.…”

Approaches to quantifying the electronic and steric properties of metallodithiolates as ligands in coordination chemistry

“…Thus, the indirect interactions of steric and electronic effects of what we will define as the endo metal (M, that within the N 2 S 2 site) on the residual S-donor ability to the exo metal (M', that attached to one or both of the cis−dithiolates) is of significance, and questions related to this coordination environment are the object of this report. [4][5][6][7][8], and as monodentate ligands to W(CO) 5 [9], Fe(CO) 4 [10], and Ni(CO) 3 acceptors [11], wherever valid comparisons may be found. Values derived from three methods of quantifying steric bulk are listed in Table 1: a) the "solid angle" [12]; b) our modification of Tolman's ligand cone angle; and c) Nolan's percent buried volume (%V bur ) [13].…”