Large Ligand Folding Distortion in an Oxomolybdenum Donor–Acceptor Complex

Abstract

Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO(SPh)2(iPr2Dto) (where iPr2Dto is N,N′-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° “envelope” type fold of the five member dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ~18,000 cm−1 is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL′CT) transition that also possesses Mo(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo(x2−y2) orbital character derives from a strong pseudo Jahn-Teller effect, which drives the large fold angle distortion to yield a double well potential in the electronic ground state.

The Impact of Ligand Oxidation State and Fold Angle on the Charge Transfer Processes of MoIVO‐Dithione Complexes

“…In this work, we describe the synthesis, spectroscopic, and redox properties of a series of oxo‐Mo(IV) compounds of the type [MoOCl(R 2 Dt 0 ) 2 ][X], ( 1 and 2 ), and MoO( p ‐SC 6 H 4 Y) 2 (R 2 Dt 0 ), ( 3 and 4 ) (R=Me, i Pr; X=PF 6 , SbF 6 , BF 4 ; Y=H, Cl, F, CF 3 , Me, t Bu, OMe,) (Scheme 1). Compounds 1 a and 3 a have been previously reported, [3b,c] and here we disclose the complete set of complexes. In rare examples, where molybdenum complexes possess fully oxidized Dt 0 ligands, the lowest energy charge transfer band is influenced by the ligand oxidation state.…”

“…The structural and spectroscopic properties of six‐coordinate tris and four coordinate square planar complexes possessing Dt 2− ligands have been comprehensively investigated [2a] . We [3a,b,d,4] and others [3f,g,5] have contributed to the development of metal complexes with oxidized Dt 0 to discern their electronic properties.…”

Metal–Dithiolene Bonding Contributions to Pyranopterin Molybdenum Enzyme Reactivity

“…Experimental investigation of the electronic structures of the Mo centers of enzymes is difficult because of the intense absorptions from other chromophores (e.g., the b-type heme in sulfite oxidase and iron sulfur centers and FAD in xanthine oxidase) [37][38][39][40][41]. However, the effects of dithiolene coordination on electronic structure have been investigated for model oxo-Mo(V) compounds ( Figure 6) by electronic absorption, XAS, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies [12,[14][15][16][17]32,33,[42][43][44][45][46][47][48][49][50][51]. For Tp*MoO(bdt), the electronic absorptions at 19,400 cm −1 (Band 4) and 22,100 cm −1 (Band 5) are assigned to S → Mo charge transfer bands ( Figure 7A) [12].…”

“…This cofactor is also found in anaerobic tungsten enzymes, and it may be one of the most ancient cofactors in biology [5]. The study of metal-dithiolene compounds (metallodithiolenes) has undergone a recent renaissance, with their synthesis, geometric structure, spectroscopy, bonding, and electronic structure having been recently highlighted [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Here, we briefly review the discovery of metallodithiolene compounds [13,21].…”

Syntheses, spectroscopic, redox, and structural properties of homoleptic Iron(III/II) dithione complexes

“…However, a homoleptic Fe III DT 0 complex is yet to be reported. As a part of our ongoing efforts to understand the fundamental coordination chemistry of Dt 0 ligands, we have reported coordination chemistry of Zn, 38 Cu, 39 Ni 40 and Mo [41][42][43][44] complexes. Here we report the synthesis, structure and redox properties of homoleptic [Fe II (Dt 0 ) 3 ] 2+ and [Fe III (Dt 0 ) 3 ] 3+ complexes.…”