Computational Study of Iron Bis(dithiolene) Complexes: Redox Non-Innocent Ligands and Antiferromagnetic Coupling

The molecular and electronic structure of monomeric ([Fe(S2C2H2)2]z, [Fe(S2C2(C6H4-p-OCH3)2)2]z) and dimeric ([{Fe(S2C2H2)2}2]z) iron bis(dithiolene) complexes, and of their phosphine adducts ([(PH3)Fe(S2C2H2)2]z, [(P(C6H5)3)Fe(S2C2H2)2]z, [(PH3)Fe(S2C2(C6H4-p-OCH3)2)2]z), carrying various charges (z = 0, 1−, 2−), have been investigated by density functional theory (DFT). Net total spin polarization values S of zero, two, and four have been considered for all neutral model compounds and their dianions, whereas all monoanions have been examined with net total spin polarization values S of one, three, and five. The DFT calculations utilized the pure functional BP86, as well as the hybrid functionals B3LYP and B3LYP*. For the monomers, the calculations reveal the presence of redox non-innocent dithiolene ligands and antiferromagnetic coupling between the ligands and the metal center. For the dimers, complexes with antiferromagnetically coupled iron centers have been found to represent structures of low energy, if not lowest energy structures. The spin-coupling constant of [{Fe(S2C2H2)2}2]2− is calculated as J = −230 cm−1. On the basis of the computational results, a model for reversible, electrochemically controlled binding and release of phosphine ligands to iron bis(dithiolene) complexes is proposed. Only BP86 and B3LYP* results, but not those of B3LYP calculations, are in qualitative agreement with experimental findings. BP86 calculations provide the best quantitative match in comparison with the experiment

Synthesis and Structures of Bis(dithiolene)molybdenum Complexes Related to the Active Sites of the DMSO Reductase Enzyme Family

Structural analogues of the reduced (Mo(IV)) sites of members of the DMSO reductase family of molybdoenzymes are sought. These sites usually contain two pterin−dithiolene cofactor ligands and one protein-based ligand. Reaction of [Mo(MeCN)3(CO)3] and [Ni(S2C2R2)2] affords the trigonal prismatic complexes [Mo(CO)2(S2C2R2)2] (R = Me (1), Ph (2)), which by carbonyl substitution serve as useful precursors to a variety of bis(dithiolene)molybdenum(IV,V) complexes. Reaction of 1 with Et4NOH yields [MoO(S2C2Me2)2]2- (3), which is readily oxidized to [MoO(S2C2Me2)2]1- (4). The hindered arene oxide ligands ArO- afford the square pyramidal complexes [Mo(OAr)(S2C2R2)2]1- (5, 6). The ligands PhQ- afford the trigonal prismatic monocarbonyls [Mo(CO)(QPh)(S2C2Me2)2]1- (Q = S (8), Se (12)) while the bulky ligand ArS- forms square pyramidal [Mo(SAr)(S2C2R2)2]1- (9, 10). In contrast, reactions with ArSe- result in [Mo(CO)(SeAr)(S2C2R2)2]1- (14, 15), which have not been successfully decarbonylated. Other compounds prepared by substitution reactions of 1 and 2 include the bridged dimers [Mo2(μ-Q)2(S2C2Me2)4]2- (Q = S (7), Se (11)) and [Mo2(μ-SePh)2(S2C2Ph2)4]2- (13). The complexes 1, 3−5, 7−10, 12−14, [Mo(S2C2Me2)3] (16), and [Mo(S2C2Me2)3]1- (17) were characterized by X-ray structure determinations. Certain complexes approach the binding arrangements in at least one DMSO reductase (5/6) and its Ser/Cys mutant, and in dissimilatory nitrate reductases (9/10). This investigation provides the initial demonstration of the new types of bis(dithiolene)molybdenum(IV) complexes available through [Mo(CO)2(S2C2R2)2] precursors, some of which will be utilized in reactivity studies. (Ar = 2,6-diisopropylphenyl or 2,4,6-triisopropylphenyl.

Synthesis and Structures of Cuprous Triptycylthiolate Complexes

A synthesis of 1-(thioacetyl)­triptycene (5), a convenient protected form of 1-(thiolato)­triptycene [STrip]−, is described, a key transformation being the high yield conversion of tert-butyl 1-triptycenyl sulfide (8) to 5 by a protocol employing BBr3/AcCl. Syntheses of the two-coordinate copper­(I) compounds [Bu4N]­[Cu­(STrip)2], [Bu4N]10, and [(Cu­(IMes)­(STrip)] (13) proceed readily by chloride displacement from CuCl and [Cu­(IMes)­Cl], respectively. Reaction of 10 with Ph3SiSH or Me3SiI produces the heteroleptic species [Cu­(STrip)­(SSiPh3)]− (11) and [Cu­(STrip)­I]− (12), detected by mass spectrometry, in mixture with the homoleptic bis­(thiolate) anions. Structural identification by X-ray crystallography of the ligand precursor molecules 9-(thioacetyl)­anthracene (4, triclinic and orthorhombic polymorphs), tert-butyl 9-anthracenyl sulfide (7), 5, and tert-butyl 1-triptycenyl sulfide (8) are presented. Crystallographic characterization of bis­(9-anthracenyl)­sulfide (3), which features a C–S–C angle of 104.0° and twist angle of 54.8° between anthracenyl planes, is also given. A crystal structure of [Bu4N]­[(STrip)], [Bu4N]9, provides an experimental measure of 144.6° for the ligand cone angle. The crystal structures of [Bu4N]10 and 13 are reported, the former of which reveals an unexpectedly small C–S···S–C torsion angle of ∼41° (average of two values), which confers a near “cis” disposition of the triptycenyl groups with respect the S–Cu–S axis. This conformation is governed by interligand π···π and CH···π interactions. A crystal structure of an adventitious product, [Bu4N]­[(Cu-STrip)6(μ6-Br)]·[Bu4N]­[PF6], [Bu4N]14·[Bu4N]­[PF6] is described, which reveals a cyclic hexameric structure previously unobserved in cuprous thiolate chemistry. The Cu6S6 ring displays a centrosymmetric cyclohexane chair type conformation with a Br– ion residing at the inversion center and held in place by apparent soft–soft interactions with the Cu­(I) ions

Gold(III)-Catalyzed Double Hydroamination of <i>o</i>-Alkynylaniline with Terminal Alkynes Leading to <i>N</i>-Vinylindoles

A highly efficient double-hydroamination reaction of o-alkynylanilines with terminal alkynes leading to N-alkenylindoles was developed by using gold(III) as a catalyst under neat conditions

Polyunsaturated Dicarboxylate Tethers Connecting Dimolybdenum Redox and Chromophoric Centers: Syntheses, Structures, and Electrochemistry

Compounds with two quadruply bonded Mo24+ units, Mo2(DAniF)3 (DAniF = N,N ‘-di-p-anisylformamidinate), linked by unsaturated dicarboxylate dianions of various lengths have been prepared and their spectroscopic and electrochemical properties studied. As identified by the dicarboxylate linkers, these compounds are maleate (7), allene-1,3-dicarboxylate (10), cis,cis-muconate (11), trans,trans-muconate (12), octa-2,4,6-trans,trans,trans-hexatriene-1,8-dioate (tamuate, 13), and deca-2,4,6,8-trans,trans,trans,trans-octatetraene-1,10-dioate (texate, 14). The latter three molecules complete the five-membered (all trans) series [Mo2(DAniF)3](O2C(CHCH)nCO2)[Mo2(DAniF)3] (n = 0−4). Several unsymmetrical paddlewheel compounds of the type Mo2(DAniF)3(O2CX) (X = C⋮CH (3), CHCH2 (4), (E)-CHCHCHCH2 (5)) have also been prepared for comparison to the molecules in which there are linked Mo2 units. The precursors [Mo2(DAniF)3(MeCN)2](BPh4), [1]BPh4, and Mo2(DAniF)3Cl(MeCN) (2) have also been isolated and characterized. The structures of all new molecules have been established by X-ray crystallography, including the methyl esters of various carboxylates used as ligands. All of the linked molecules have been examined by cyclic and differential pulse voltammetry, and ΔE1/2 values, the separation between successive Mo24+/Mo25+ oxidations, have been determined. Those compounds with highly unsaturated, fully conjugated linkers demonstrate electrochemical communication from end-to-end that is more persistent over distance than is accounted for by an electrostatic interaction alone, implying that the π system of these dicarboxylate linkers is mediating communication. In the series [Mo2(DAniF)3](O2C(CHCH)nCO2)[Mo2(DAniF)3] (n = 0−4), the first oxidation potential shifts progressively to less positive values due to an increasing contribution of the polyolefinic α,ω-dicarboxylate to the molecular orbital undergoing oxidation. This first oxidation potential approaches a limiting value of 63 mV (vs Ag/AgCl) as n becomes infinitely long. Compound 11 can be photoisomerized to 12 in a process that is affected by the presence of the Mo24+ units, as the analogous rearrangement of dimethyl cis,cis-muconate is faster

Synthesis and Structures of Bis(dithiolene)molybdenum Complexes Related to the Active Sites of the DMSO Reductase Enzyme Family

Structural analogues of the reduced (Mo(IV)) sites of members of the DMSO reductase family of molybdoenzymes are sought. These sites usually contain two pterin−dithiolene cofactor ligands and one protein-based ligand. Reaction of [Mo(MeCN)3(CO)3] and [Ni(S2C2R2)2] affords the trigonal prismatic complexes [Mo(CO)2(S2C2R2)2] (R = Me (1), Ph (2)), which by carbonyl substitution serve as useful precursors to a variety of bis(dithiolene)molybdenum(IV,V) complexes. Reaction of 1 with Et4NOH yields [MoO(S2C2Me2)2]2- (3), which is readily oxidized to [MoO(S2C2Me2)2]1- (4). The hindered arene oxide ligands ArO- afford the square pyramidal complexes [Mo(OAr)(S2C2R2)2]1- (5, 6). The ligands PhQ- afford the trigonal prismatic monocarbonyls [Mo(CO)(QPh)(S2C2Me2)2]1- (Q = S (8), Se (12)) while the bulky ligand ArS- forms square pyramidal [Mo(SAr)(S2C2R2)2]1- (9, 10). In contrast, reactions with ArSe- result in [Mo(CO)(SeAr)(S2C2R2)2]1- (14, 15), which have not been successfully decarbonylated. Other compounds prepared by substitution reactions of 1 and 2 include the bridged dimers [Mo2(μ-Q)2(S2C2Me2)4]2- (Q = S (7), Se (11)) and [Mo2(μ-SePh)2(S2C2Ph2)4]2- (13). The complexes 1, 3−5, 7−10, 12−14, [Mo(S2C2Me2)3] (16), and [Mo(S2C2Me2)3]1- (17) were characterized by X-ray structure determinations. Certain complexes approach the binding arrangements in at least one DMSO reductase (5/6) and its Ser/Cys mutant, and in dissimilatory nitrate reductases (9/10). This investigation provides the initial demonstration of the new types of bis(dithiolene)molybdenum(IV) complexes available through [Mo(CO)2(S2C2R2)2] precursors, some of which will be utilized in reactivity studies. (Ar = 2,6-diisopropylphenyl or 2,4,6-triisopropylphenyl.

Polyunsaturated Dicarboxylate Tethers Connecting Dimolybdenum Redox and Chromophoric Centers: Syntheses, Structures, and Electrochemistry

Compounds with two quadruply bonded Mo24+ units, Mo2(DAniF)3 (DAniF = N,N ‘-di-p-anisylformamidinate), linked by unsaturated dicarboxylate dianions of various lengths have been prepared and their spectroscopic and electrochemical properties studied. As identified by the dicarboxylate linkers, these compounds are maleate (7), allene-1,3-dicarboxylate (10), cis,cis-muconate (11), trans,trans-muconate (12), octa-2,4,6-trans,trans,trans-hexatriene-1,8-dioate (tamuate, 13), and deca-2,4,6,8-trans,trans,trans,trans-octatetraene-1,10-dioate (texate, 14). The latter three molecules complete the five-membered (all trans) series [Mo2(DAniF)3](O2C(CHCH)nCO2)[Mo2(DAniF)3] (n = 0−4). Several unsymmetrical paddlewheel compounds of the type Mo2(DAniF)3(O2CX) (X = C⋮CH (3), CHCH2 (4), (E)-CHCHCHCH2 (5)) have also been prepared for comparison to the molecules in which there are linked Mo2 units. The precursors [Mo2(DAniF)3(MeCN)2](BPh4), [1]BPh4, and Mo2(DAniF)3Cl(MeCN) (2) have also been isolated and characterized. The structures of all new molecules have been established by X-ray crystallography, including the methyl esters of various carboxylates used as ligands. All of the linked molecules have been examined by cyclic and differential pulse voltammetry, and ΔE1/2 values, the separation between successive Mo24+/Mo25+ oxidations, have been determined. Those compounds with highly unsaturated, fully conjugated linkers demonstrate electrochemical communication from end-to-end that is more persistent over distance than is accounted for by an electrostatic interaction alone, implying that the π system of these dicarboxylate linkers is mediating communication. In the series [Mo2(DAniF)3](O2C(CHCH)nCO2)[Mo2(DAniF)3] (n = 0−4), the first oxidation potential shifts progressively to less positive values due to an increasing contribution of the polyolefinic α,ω-dicarboxylate to the molecular orbital undergoing oxidation. This first oxidation potential approaches a limiting value of 63 mV (vs Ag/AgCl) as n becomes infinitely long. Compound 11 can be photoisomerized to 12 in a process that is affected by the presence of the Mo24+ units, as the analogous rearrangement of dimethyl cis,cis-muconate is faster

Synthesis and Structures of Bis(dithiolene)molybdenum Complexes Related to the Active Sites of the DMSO Reductase Enzyme Family

Structural analogues of the reduced (Mo(IV)) sites of members of the DMSO reductase family of molybdoenzymes are sought. These sites usually contain two pterin−dithiolene cofactor ligands and one protein-based ligand. Reaction of [Mo(MeCN)3(CO)3] and [Ni(S2C2R2)2] affords the trigonal prismatic complexes [Mo(CO)2(S2C2R2)2] (R = Me (1), Ph (2)), which by carbonyl substitution serve as useful precursors to a variety of bis(dithiolene)molybdenum(IV,V) complexes. Reaction of 1 with Et4NOH yields [MoO(S2C2Me2)2]2- (3), which is readily oxidized to [MoO(S2C2Me2)2]1- (4). The hindered arene oxide ligands ArO- afford the square pyramidal complexes [Mo(OAr)(S2C2R2)2]1- (5, 6). The ligands PhQ- afford the trigonal prismatic monocarbonyls [Mo(CO)(QPh)(S2C2Me2)2]1- (Q = S (8), Se (12)) while the bulky ligand ArS- forms square pyramidal [Mo(SAr)(S2C2R2)2]1- (9, 10). In contrast, reactions with ArSe- result in [Mo(CO)(SeAr)(S2C2R2)2]1- (14, 15), which have not been successfully decarbonylated. Other compounds prepared by substitution reactions of 1 and 2 include the bridged dimers [Mo2(μ-Q)2(S2C2Me2)4]2- (Q = S (7), Se (11)) and [Mo2(μ-SePh)2(S2C2Ph2)4]2- (13). The complexes 1, 3−5, 7−10, 12−14, [Mo(S2C2Me2)3] (16), and [Mo(S2C2Me2)3]1- (17) were characterized by X-ray structure determinations. Certain complexes approach the binding arrangements in at least one DMSO reductase (5/6) and its Ser/Cys mutant, and in dissimilatory nitrate reductases (9/10). This investigation provides the initial demonstration of the new types of bis(dithiolene)molybdenum(IV) complexes available through [Mo(CO)2(S2C2R2)2] precursors, some of which will be utilized in reactivity studies. (Ar = 2,6-diisopropylphenyl or 2,4,6-triisopropylphenyl.

Synthesis and Structures of Cuprous Triptycylthiolate Complexes

A synthesis of 1-(thioacetyl)­triptycene (<b>5</b>), a convenient protected form of 1-(thiolato)­triptycene [STrip]⁻, is described, a key transformation being the high yield conversion of <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) to <b>5</b> by a protocol employing BBr₃/AcCl. Syntheses of the two-coordinate copper­(I) compounds [Bu₄N]­[Cu­(STrip)₂], [Bu₄N]<b>10</b>, and [(Cu­(IMes)­(STrip)] (<b>13</b>) proceed readily by chloride displacement from CuCl and [Cu­(IMes)­Cl], respectively. Reaction of <b>10</b> with Ph₃SiSH or Me₃SiI produces the heteroleptic species [Cu­(STrip)­(SSiPh₃)]⁻ (<b>11</b>) and [Cu­(STrip)­I]⁻ (<b>12)</b>, detected by mass spectrometry, in mixture with the homoleptic bis­(thiolate) anions. Structural identification by X-ray crystallography of the ligand precursor molecules 9-(thioacetyl)­anthracene (<b>4</b>, triclinic and orthorhombic polymorphs), <i>tert</i>-butyl 9-anthracenyl sulfide (<b>7</b>), <b>5</b>, and <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) are presented. Crystallographic characterization of bis­(9-anthracenyl)­sulfide (<b>3</b>), which features a C–S–C angle of 104.0° and twist angle of 54.8° between anthracenyl planes, is also given. A crystal structure of [Bu₄N]­[(STrip)], [Bu₄N]<b>9</b>, provides an experimental measure of 144.6° for the ligand cone angle. The crystal structures of [Bu₄N]<b>10</b> and <b>13</b> are reported, the former of which reveals an unexpectedly small C–S···S–C torsion angle of ∼41° (average of two values), which confers a near “cis” disposition of the triptycenyl groups with respect the S–Cu–S axis. This conformation is governed by interligand π···π and CH···π interactions. A crystal structure of an adventitious product, [Bu₄N]­[(Cu-STrip)₆(μ₆-Br)]·[Bu₄N]­[PF₆], [Bu₄N]<b>14</b>·[Bu₄N]­[PF₆] is described, which reveals a cyclic hexameric structure previously unobserved in cuprous thiolate chemistry. The Cu₆S₆ ring displays a centrosymmetric cyclohexane chair type conformation with a Br^– ion residing at the inversion center and held in place by apparent soft–soft interactions with the Cu­(I) ions

Quadridentate Bridging EO₄^2- (E = S, Mo, W) Ligands and Their Role as Electronic Bridges

Three compounds containing two quadruply bonded Mo2(DAniF)3 (DAniF = N,N‘-di-p-anisylformamidinate) units linked by tetrahedral EO42- anions (E = S, Mo, W) have been prepared and characterized by crystallography and NMR. The linkers in these [Mo2(DAniF)3]2(μ-EO4) compounds hold the Mo2 units in an approximately perpendicular orientation and mediate strong electrochemical communication between them. Each of the three compounds shows two quasireversible (μ-SO4) or fully reversible (μ-MoO4, μ-WO4) features in its cyclic voltammogram corresponding to successive oxidation of each of its Mo2 units. The ΔE1/2 values are the largest thus far measured for Mo2−X−Mo2 bridged complexes and may be sufficiently large to permit isolation of the singly oxidized species