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The complexes [Pt(mdt)2] (4; mdt = methyl dithiolene, [Me2C2S2]n-), [Pt(adt)2] (5; adt = p-anisyldithiolene, [(MeO-p-C6H4)2C2S2]2-), and [Pd(adt)2] (10) have been prepared in yields of ≥ 90% via transmetalation reactions with the corresponding [R2Sn(S2C2R'2)] complexes (R = "Bu, R' = Me; R = Me, R' = C6H4-p-OMe, 3). Intrahgand C--S and C--CchclaIe bond lengths (~1.71 and ~1.40 A, respectively) obtained by X-ray crystallography show these compounds to be comprised of radical monoanions mdt*- and adt*- . The six-coordinate octahedral adducts [Pt(adt)2(dppe)J [6; dppe = 1,2-bis(diphenylphosphino)ethane], trans-[Pt(adt)2(PMe3)2] (8), and frans-[Pt(mdt)2(PMe3)2] (9) have also been prepared, and crystal structures reveal dithiolene ligands that are fully reduced ene-l,2-dithiolates (C--S and C--Cchelate = ~1.77 and 1.35 A, respectively). Reduction of the dithiolene ligand thus occurs to accommodate the +IV oxidation state typical of octahedral sixcoordinate platinum. The cyclic voltammogram of 5 shows twofully reversible reductions at --0.11 and --0.84 V in CH2C12 (vs Ag/AgCl), attributed to successive (adt*- + e- → adt2-) processes, and a reversible oxidation at +1.01 V. The cyclic voltammogram of 9 shows two reversible oxidations at +0.38 and +0.86 V, which are assigned as successive (adt2- &#8594 adt*- + e-) oxidations. Consistent with their formulation as having fully reduced dithiolene ligands, the UV--vis spectra for 6, 8, and 9 show no low-energy absorptions below 700 nm, and the S K-edge XAS spectra of 6 and 8 show dithiolene sulfur that is reduced relative to that in 5. The introduction of PMe3 to 10 did not produce the palladium analogue of 8 but rather [Pd(adt)(PMe3)2] (11) . The reaction of [PdCl2(PPh3)2] with Li2(mdt) produced a mixture of [Pd(mdt)(PPh3)2] (12, 20%) and [(Ph3P)Pd(p-l,2-mdt- S,S':S)2Pd(PPh3)] (13, 28%), with the latter having C2 symmetry with a Pd2S2 core structure folded along the S…S axis. [ABSTRACT FROM AUTHOR]

A series of reports describing the syntheses and structures of [MCl2(diazadiene)] (M = Cr, Mo, W) complexes is reassessed in the context of known chemistry of low-valent Group VI metal complexes, crystallographic trends such as M--CI bond lengths and unit cell volumes, and calculated metal--ligand bond lengths. Crystallographic data and computational results are inconsistent with any of these species being second or third row transition metal complexes. A review of the crystallographic information files accompanying the [MCl2(diazadiene)] (M = Mo, W) published structures reveals that the metal atoms were inappropriately treated with partial site occupancy factors (0.775 for Mo; 0.4005 and 0.417 for W), the effect of which was to manifest lighter-element behavior and better refinement in accord with the metal atoms' correct identity. A deliberate synthesis and characterization by X-ray diflraction of [ZnCl2(MesdadMe)] (MesdadMe = l,4-bis(2,4,6-trimethylphenyl)-2,3-dimethyl-l,4-diaza-1,3-butadiene) are reported. Refinement of this structure with the same combination of second or third row metal and offsetting partial site occupancy is shown to provide final refinement statistics essentially the same as with the correct model employing M = Zn at site occupancy 1.00. Use of the published method for synthesis of [WCl2(diazadiene)] with MesdadMe and [WBr4(MeCN)2] in lieu of [WCl4MeCN2] is shown to produce [ZnBr2(MesdadMe)], which has also been characterized by X-ray diffraction. It is concluded that the unusual putative 12-electron [MCl2(diazadiene)] (M = Cr, Mo, W) complexes are in all cases the corresponding [ZnCl2(diazadiene)] complexes, Zn having been commonly employed as reducing agent in their synthesis. [ABSTRACT FROM AUTHOR]

In recent years, a number of high-valent iron intermediates have been identified as reactive species in iron-containing metalloproteins. Inspired by the interest in these highly reactive species, chemists have synthesized Fe(iv) and Fe(v) model complexes with terminal oxo or nitrido groups, as well as a rare example of an Fe(vi)-nitrido species. In all these cases, X-ray absorption spectroscopy has played a key role in the identification and characterization of these species, with both the energy and intensity of the pre-edge features providing spectroscopic signatures for both the oxidation state and the local site geometry. Here we build on a time-dependent DFT methodology for the prediction of Fe K- pre-edge features, previously applied to ferrous and ferric complexes, and extend it to a range of Fe(iv), Fe(v) and Fe(vi) complexes. The contributions of oxidation state, coordination environment and spin state to the spectral features are discussed. These methods are then extended to calculate the spectra of the heme active site of P450 Compound II and the non-heme active site of TauD. The potential for using these methods in a predictive manner is highlighted. [ABSTRACT FROM AUTHOR]

Cyclodiphosphazanes having hemilabile ponytails such as cis-[tBuNP(OC6H4OMe-o)]2 (2), cis-[tBuNP(OCH2CH2-OMe)]2 (3), cis-[tBuNP(OCH2CH2SMe)]2 (4), and cis-[tBuNP(OCH2CH2NMe2))2 (5) were synthesized by reacting cis-[tBuNPCl]2 (1) with corresponding nucleophiles. The reaction of 2 with [M(COD)Cl2] afforded cis-[MCl2(2)2] derivatives (M = Pd (6), Pt (7)), whereas, with [Pd(NCPh)2C]2], trans-[MCl2(2)2] (8) was obtained. The reaction of 2 with [Pd(PEt3)Cl2]2, [Ru(η6p-cymene)Cl2]2, and [M(COD)Cl]2 (M = Rh, Ir) afforded mononuclear complexes of Pd(II) (9), Ru(II) (11), Rh(I) (12), and Ir(l) (13) irrespective of the stoichiometry of the reactants and the reaction condition. In the above complexes the cyclodiphosphazane acts as a monodentate ligand. The reaction of 2 with [PdCl(η³-C3H5))2 afforded binuclear complex [(PdCl(η³-C3H5))2{(tBuNP(OC6H4OMe-o))2-κP}] (10). The reaction of ligand 3 with [Rh(CO)2Cl]2 in 1:1 ratio in CH3CN under reflux condition afforded tetranuclear rhodium(1) metallamacrocycle (14), whereas the ligands 4 and 5 afforded bischelated binuclear complexes 15 and 16, respectively. The crystal structures of 8, 9, 12, 14, and 16 are reported. [ABSTRACT FROM AUTHOR]

Dimetallic compounds I(P-P)M(S2C6H2S2)M(P-P)] (M=Ni, Pd; P-P=chelating bis(phosphine), 3a-3f) are prepared from OCS2C6H2S2CO or nBu2SnS2C6H2S2SnnBu2, which are protected forms of 1,2,4,5-benzenetetrathiolate. Selective monodeprotections of OCS2C6H2S2CO or nBu2SnS2C6H2S2SnnBu2 lead to [(P-P)Ni(S2C6- H2S2CO)] or [(P-P)Ni(S2C6H2S2SnnBu2)]; the former is used to prepare trimetallic compounds [(dcpe)Ni(S2C6H2S2)M(S2C6H2S2)Ni(dcpe)] (M = Ni (6a) or Pt (6b); dcpe = 1 ,2-bis(dicyclohexylphosphino)ethane). Compounds 3a-3f are redox active and display two oxidation processes, of which the first is generally reversible. Dinickel compound [(dcpe)Ni(S2C6H2S2)Ni(dcpe)] (3d) reveals two reversible oxidation waves with ΔE½=0.66 V, corresponding to κC of 1.6 x 1011 for the mixed valence species. Electrochemical behavior is unstable to repeated scanning in the presence of [Bu4N][PF6] electrolyte but indefinitely stable with Na[BArF24] (BArF24 = tetrakis(3, 5-bis(frifluoromethyl)phenyl)borate), suggesting that the radical cation generated by oxidation is vulnerable to reaction with PF6-. Chemical oxidation of 3d with [Cp2Fe][BArF24] leads Information of [3d][BArF24]. Structural identification of [3d][BArF24] reveals appreciable shortening and lengthening of C-S and C-C bond distances, respectively, within the tetrathioarene fragment compared to charge neutral 3d, indicating this to be the redox active moiety. Attempted oxidation of [(dppb)Ni(S2C6H2S2)Ni(dppb)] (3c) (dppb = 1 ,2-bis(diphenylphosphino)benzene) with AgBArF24 produces [[(dppb)Ni(S2C6H2S2)Ni(dppb)]2(μ-Ag2)][BArF24]2, [4c][BArF24]2, in which no redox chemistry has occurred. Crystal structures of bis(disulfide)-linked compounds [(P-P)Ni(S2C6H2(u-S2)2C6H2S2)Ni(P-P)] are reported. Near IR spectroscopy upon cationic [3d]+ and neutral 6a reveals multiple intense absorptions in the 95O-14OO nm region. Time-dependent density functional theory (DFT) calculations on a 6a model compound indicate that these absorptions are transitions between ligand-based π-type orbitals that have significant contributions from the sulfur p orbitals. [ABSTRACT FROM AUTHOR]

Heteroleptic bis(dithiolene)-phosphine iron and cobalt complexes [Fe(adt) 2 (PMe 3 )] ( 1 ) and [Co(adt) 2 (PMe 3 )] ( 2 ) (adt = para -anisyldithiolene) have been synthesized from corresponding bis(dithiolene) dimers [M 2 (adt) 4 ] 2 (M = Fe, Co) by reacting with excess PMe 3 in dichloromethane. Solid-state structures of 1 and 2 have been determined by single crystal X-ray crystallography, and the dithiolene ligands C S (≈1.72 Å) and C C (≈1.37 Å) bond distances reveal the coordination of π-radical monoanionic dithiolene (adt• 1− ) ligands to metal centers. Intense low energy ligand-to-ligand-charge transfer (LLCT) absorption band (743 nm for 1 ; 905 nm for 2 ) in UV–vis spectra and characteristic ν (C S•) (1168 cm −1 for 1 ; 1170 cm −1 for 2 ) in IR spectra affirms coordination of π-radical monoanionic dithiolenes to divalent metal ions. The cyclic voltammogram of 1 and 2 shows reversible oxidation and reduction waves attributed to M II → M III + e − (+0.52 V for 1 ; +0.29 V for 2 ) and adt• 1− + e − → adt 2− (−0.63 V for 1 ; −0.46 V for 2 ) redox process respectively. Comprehensive structural and spectroscopic investigations conclude, [M 2 III (adt 2− ) 2 (adt• 1- ) 2 ] → 2 [M II (adt• 1- ) 2 (PMe 3 )] intramolecular redox interplay during phosphine coordination induced cleavage of homoleptic bis(dithiolene) dimers to produce square pyramidal complexes. [ABSTRACT FROM AUTHOR]