Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study

Abstract

Heterotrimetallic complexes with (N 2 S 2 )M metallodithiolates, M = Ni 2+ , [Fe(NO)] 2+ , and [Co(NO)] 2+ , as bidentate chelating ligands to a central trans-Cr(NO)(MeCN) unit were characterized as the first members of a new class, NiCrNi, FeCrFe, CoCrCo. The complexes exhibit a cisoid structural topology, ascribed to the stereoactivity of the available lone pair(s) on the sulfur donors, resulting in a dispersed, electropositive pocket from the N/N and N/S hydrocarbon linkers wherein the Cr-NO site is housed. Computational studies explored alternative isomers (transoid and inverted cisoid) that suggest a combination of electronic and steric effects govern the geometrical selectivity. Electrostatic potential maps readily display the dominant electronegative potential from the sulfurs which force the NO to the electropositive pocket. The available S lone pairs work in synergy with the π-withdrawing ability of NO to lift Cr out of the S 4 plane toward the NO and stabilize the geometry. The metallodithiolate ligands bound to Cr(NO) thus find structural consistency across the three congeners. Although the dinitrosyl [(bme-dach)Co(NO)-Mo(NO)(MeCN)-(bme-dach)Co(MeCN)][PF 6 ] 2 (CoMoCo′) analogue displays chemical noninnocence and a partial Mo−Co bond toward (N 2 S 2 )Co′(NCCH 3 ) in an "asymmetric butterfly" topology [Guerrero-Almaraz, P. et al. Inorg. Chem. 2021, 60(2121), 15975−15979], the stability of the {Cr(NO)} 5 unit prohibits such bond rearrangement. Magnetism and EPR studies illustrate spin coupling across the sulfur thiolate sulfur bridges.

Development of (NO)Fe(N2S2) as a Metallodithiolate Spin Probe Ligand: A Case Study Approach

“…In search of different arrangement centers, we noted that synthetic efforts from the Richards and Louttit groups had produced a series of diphosphine ligands bound to {Mo­(NO)} 6 and {Cr­(NO)} 5 in a trans-configuration (Figure A). , Similar approaches with the Ni­(N 2 S 2 ) and (NO)­Fe­(N 2 S 2 ) complexes as ligands found that the thermodynamically stable trimetallic products linked with {Cr­(NO)} 5 were in the cissoid arrangement; the­[(NO)­Fe­(N 2 S 2 )] 2 Cr­(NO)­(CH 3 CN)] 2+ or [ FeCrFe ] 2+ product is shown in Figure B. The unique stereochemical behavior found in the “uncommon” isomer emerges from the additional lone pair(s) interactions on the sulfur donor atoms …”

“…Inorg. Au 2023 , 3 , 393 . A central trans -Cr­(NO)­(MeCN) radical unit positions two (NO)­Fe­(N 2 S 2 ), S = 1/2 metalloligands in a cissoid structure 6 Å apart.…”

“…(B) Optimized structure of [ NiCrNi ] 2+ with its ESP map shown in a similar topology. Adapted with permission from ref . Copyright 2023 American Chemistry Society.…”

“…(C) ChemDraw depiction of the residual S-lone pairs and Cr­(NO) π-orbitals in the cissoid arrangement. Adapted with permission from ref . Copyright 2023 American Chemistry Society.…”

A single carbon atom controls the geometry and reactivity of CoII(N2S2) complexes

“…2 Limited information is available for M = Co( ii ) or Co( iii )(NO) − , owing to its chemical non-innocence (volatility) involving NO transfer, sometimes accompanied by Co exchange with other metals or uptake of solvent donors, resulting in intricate and unpredictable formulations. 3…”