Cymantrene radical cation family: spectral and structural characterization of the half-sandwich analogues of ferrocenium ion

The anodic one-electron oxidation of three members of the half-sandwich family of piano-stool compounds MnCp (gamma)(CO) 3, where Cp (gamma) is a generic cyclopentadienyl ligand, has been studied in a CH 2Cl 2/[NBu 4][TFAB] electrolyte (TFAB = [B(C6F5) 4] (-)). The long-sought 17 e (-) radical cation of the parent complex MnCp(CO) 3 (cymantrene, 1, E 1/2 = 0.92 V vs ferrocene) has been shown to be persistent in solutions that use weakly coordinating anions in place of more nucleophilic traditional electrolyte anions. Spectroscopically characterized for the first time, 1 (+) was shown to absorb in the visible (530 nm), near-IR (2066 nm), and IR (2118, 1934 cm (-1)) regions. It was ESR-active at low temperatures (g parallel = 2.213, g perpendicular = 2.079, A parallel (Mn) = 79.2 G, A perpendicular (Mn) = 50 G) and NMR active at room temperature (delta = 22.4 vs TMS). The radical cations of the Cp-functionalized analogues, Mn(eta (5)-C5H 4NH2)(CO) 3, 2, E 1/2 = 0.62 V, and MnCp*(CO) 3 (Cp*= eta (5)-C 5Me 5, 3), E 1/2 = 0.64 V, were generated electrochemically as well by the chemical oxidant [ReCp(CO) 3] (+). The structures of 2 (+) and 3 (+) were determined by X-ray crystallographic studies of their TFAB salts. Compared to the structures of the corresponding neutral compounds, the cations showed elongated Mn-C(O) bonds and shortened C-O bonds, displaying the effect of diminished metal-to-CO backbonding. The bond-length changes in the Mn(CO) 3 moiety were much larger in 3 (+) (avg changes, Mn-C(O) = + 0.142 A, C-O = -0.063 A) than in 2 (+) (avg changes, Mn-C(O) = + 0.006 A, C-O = -0.003 A). Although there were only minor changes in the metal-to-center ring distances upon oxidation of either 2 or 3, there was decidedly less bending of the C(N) atom out of the cyclopentadienyl plane in 2 (+) compared to 2. The optical, vibrational, and magnetic resonance spectra of radicals 2 (+) and 3 (+) were also observed. The spectral data argue for the SOMOs of the 17-electron species being largely located on the Mn(CO) 3 moiety, having 40-50% Mn d-orbital character, with the ground states of the radicals, most likely (2)A', lying close in energy (within about 6000 cm (-1)) to excited states that are responsible for their rapid electronic relaxations. The cymantrenyl moiety is proposed as an anodic redox tag (or label) having physical and chemical properties that are significantly different from those of its ferrocenyl analogue.     

Characterization and reactions of previously elusive 17-electron cations: electrochemical oxidations of (C(6)H(6))Cr(CO)(3) and (C(5)H(5))Co(CO)(2) in the presence of [B(C(6)F(5))(4)](-)

The electrochemical oxidations of (C6H6)Cr(CO)3, 1, and (C5H5)Co(CO)2, 2, when carried out in CH2Cl2/[NBu4][B(C6F5)4], allow the physical or chemical characterization of the 17-electron cations 1+ and 2+ at room temperature. The generation of 1+ on a synthetic time scale permits an electrochemical "switch" process involving facile substitution of CO by PPh3 as a route to (C6H6)Cr(CO)2PPh3. The radical 2+ undergoes a second-order reaction to give a product assigned as the metal-metal bonded dimer dication [Cp2Co2(CO)4]2+. The new anodic chemistry of these often-studied 18-electron compounds is made possible by increases in the solubility and thermal stability of the cation radicals in media containing the poorly nucleophilic anion [B(C6F5)4]-, TFAB.     

Dinuclear oxidative addition of N-H and S-H bonds at chromium. Reaction of (*)Cr(CO)(3)(C(5)Me(5)) with [o-(HA)C(6)H(4)S-Cr(CO)(3)(C(5)Me(5))] (A = S,NH) yielding [eta(2)-o-(mu-A)C(6)H(4)S-Cr(C(5)Me(5))](2) and H-Cr(CO)(3)(C(5)Me(5))

Reaction of the 17-electron radical (*)Cr(CO)(3)Cp* (Cp* = C(5)Me(5)) with 0.5 equiv of 2-aminophenyl disulfide [(o-H(2)NC(6)H(4))(2)S(2)] results in rapid oxidative addition to form the initial product (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp*. Addition of a second equivalent of (*)Cr(CO)(3)Cp* to this solution results in the formation of H-Cr(CO)(3)Cp* as well as (1)/(2)[[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2). Spectroscopic data show that (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp* loses CO to form [eta(2)-(o-H(2)N)C(6)H(4)S]Cr(CO)(2)Cp*. Attack on the N-H bond of the coordinated amine by (*)Cr(CO)(3)Cp* provides a reasonable mechanism consistent with the observation that both chelate formation and oxidative addition of the N-H bond are faster under argon than under CO atmosphere. The N-H bonds of uncoordinated aniline do not react with (*)Cr(CO)(3)Cp*. Reaction of the 2 mol of (*)Cr(CO)(3)Cp* with 1,2-benzene dithiol [1,2-C(6)H(4)(SH)(2)] yields the initial product (o-HS)C(6)H(4)S-Cr(CO)(3)Cp and 1 mol of H-Cr(CO)(3)Cp*. Addition of 1 equiv more of (*)Cr(CO)(3)Cp to this solution also results in the formation of 1 equiv of H-Cr(CO)(3)Cp*, as well as the dimeric product (1)/(2)[[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2). This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination of the second thiol group prior to oxidative addition. The crystal structures of [[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2) and [[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2) are reported.     

Ten-electron coordination and reactivity of an arylphosphinidene ligand

Photochemical decarbonylation of [Mo2Cp2(mu-PR*)(CO)4] (Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) gives [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2], which shows the first example of a remarkable 10-electron donor arylphosphinidene ligand which bridges two Mo atoms through its phosphorus atom while being pi-bonded to one Mo center through the six carbon atoms of the aryl ring. This causes a severe pyramidal distortion of the P-bound C atom. The complex adds CO to give [Mo2Cp2(mu-kappa1:kappa1,eta4-PR*)(CO)3], which has an 8-electron donor PR* ligand, and then the parent complex [Mo2Cp2(mu-PR*)(CO)4]. Protonation of [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2] gives the hydride [Mo2Cp2(H)(mu-kappa1:kappa1,eta6-PR*)(CO)2]+, which undergoes P-C bond cleavage and hydride migration, affording the phosphido cation [Mo2Cp2(mu-P)(eta6-R*H)(CO)2]+.     

Increased reactivity of the *Cr(CO)3(C5Me5) radical with thiones versus thiols: a theoretical and experimental investigation

2-pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical *Cr(CO)3Cp (where Cp*=C5Me5), yielding hydride H-Cr(CO)3Cp* and thiolate (eta1-2mp)Cr(CO)3Cp*. In a slower secondary reaction, (eta1-2mp)Cr(CO)3Cp* loses CO generating the N,S-chelate complex (eta2-2mp)Cr(CO)2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with *Cr(CO)3Cp* (abbreviated *Cr) in toluene best fits rate=kobs[H-2mp][*Cr]; kobs(288 K)=22 +/- 4 M(-1) s(-1); DeltaH++=4 +/- 1 kcal/mol; DeltaS++=- 40 +/- 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH=1.06 +/- 0.10). The rate of decarbonylation of (eta1-2mp)Cr(CO)3Cp* forming (eta2-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K)=3.1x10(-4) s(-1), DeltaH++=23 +/- 1 kcal/mol, and DeltaS++=+ 5.0 +/- 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with *Cr(CO)3Cp* in THF and CH2Cl2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [*(S=C5H4N-H)Cr(CO)3Cp*] versus [*(H-S-C6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H* radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by approximately 30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H* to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H* or HS* without barrier.     

Aurophilic self-assembly of a Mo4Au2 phosphinidene complex with an unprecedented H-shaped planar metal core

The isomers [Mo2Cp2(mu-kappa(1):kappa(1),eta(6)-PR*)(CO)2] (1) and [Mo2Cp(mu-kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)] (2) (Cp = eta(5)-C5H5; R* = 2,4,6-C6H2(t)Bu3) react with [AuCl(THT)] and with the cation [Au(THT)2](+) (THT = tetrahydrothiophene) to give phosphinidene-bridged Mo2Au complexes resulting from the addition of an AuCl or Au(THT)(+) electrophile to their multiple P-Mo bonds. Removal of the Cl(-) or THT ligand from these derivatives causes a dimerization of the trinuclear structures to give the cationic derivative [{AuMo2Cp(mu3-kappa(1):kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)}2](2+), which displays a novel H-shaped metal core held by strong Mo-Au dative bonds [2.768(1) A] and an aurophilic interaction [Au-Au = 3.022(1) A].     

Synthesis and structure of heterometallic complexes (RhFe, CoFe) containing bridging 1,2-dicarba-closo-dodecarborane-1,2-dichalcogenolato ligands

The prototype hetero-binuclear complexes containing metal-metal bonds, {CpRh[E2C2(B10H10)]}[Fe(CO)3] (Cp = Cp* = eta 5-Me5C5, E = S(5a), Se(5b); Cp = Cp = eta 5-1,3-tBu2C5H3, E = S(6a), Se(6b)) and {CpCo[E2C2(B10H10)]}[Fe(CO)3] (Cp = Cp* = eta 5-Me5C5, E = S(7a), Se(7b); Cp = Cp = eta 5-C5H5, E = S(8a), Se(8b)) were obtained from the reactions of 16-electron complexes CpRh[E2C2(B10H10)] (Cp = Cp*, E = S(1a), Se(1b); Cp = Cp, E = S(2a), Se(2b)), CpCo[E2C2(B10H10)] (Cp = Cp*, E = S(3a), Se(3b); Cp = Cp, E = S(4a), Se(4b)) with Fe(CO)5 in the presence of Me3NO. The molecular structures of {Cp*Rh[E2C2(B10H10)]}[Fe(CO)3] (E = S(5a), Se(5b)), {CpRh[S2C2(B10H10)]}[Fe(CO)3] (6a) {Cp*Co[S2C2(B10H10)]}[Fe(CO)3] (7a) and {CpCo[S2C2(B10H10)]}[Fe(CO)3] (8a) have been determined by X-ray crystallography. All these complexes were characterized by elemental analysis and IR and NMR spectra.     

Synthesis of ortho- and meta-Re(I)-metallocarboranes in water

A series of metallocarboranes of the types rac-[M(CO)3(eta(5)-7-R-7,8-C2B9H11)]-, rac-[M(CO)3(eta(5)-7-R-8-R'-7,8-C2B9H11)]-, and rac-[M(CO)3(eta(5)-7-R-7,9-C2B9H11)]- (M=Re) were prepared by reacting [NEt4]2[Re(CO)3Br3] or [Re(CO)3(OH2)3]Br with the corresponding carboranes in the presence of aqueous solutions of either alkali metal or tetraalkylammonium fluoride salts. Carborane derivatives that were investigated included those containing pyridine, amino, carboxylic acid, carbohydrate, and aryl substituents. During the course of the research, it was discovered that Re metallocarboranes can be prepared directly from the respective closo-clusters under similar reaction conditions used with nido-carboranes. Reaction yields ranged from modest to excellent depending on the carborane isomer and the nature of the cage substituent(s). A crystal structure of an amine-substituted Re metallocarborane was obtained where the complex crystallized in the orthorhombic space group P2(1)2(1)2(1) with a=8.982(2) A, b=11.563(3) A, c=16.811(4) A, alpha=beta=gamma=90 degrees, V=1746.1(7) A3, Z=4, and R1=0.0684.     

Tunable supramolecular synthons and versatile, water-soluble building blocks for crystal engineering:

It is shown that the water-soluble dicarboxylic cationic acid [(eta5-C5H4COOH)2Co(III)]+ (1) is an extremely versatile building block for the construction of organometallic crystalline edifices. Removal of one proton from 1 leads to formation of the neutral zwitterion [(eta5-C5H4COOH)(eta5-C5H4COO)Co(III)] (2), while further deprotonation leads to formation of the dicarboxylate monoanion [(eta5-C5H4COO)2Co(III)]- (3). Compounds 1. 2 and 3 possess different hydrogen-bonding capacity and participate in a variety of hydrogen-bonding networks. The cationic form 1 has been characterised as its [PF6]- and Cl- salts 1-[PF6] and 1-Cl.H2O, as well as in its co-crystal with urea, 1-Cl.3(NH2)2CO, and with the zwitterionic form 2, [(eta5-CH4COOH)(eta5-C5H4COO)Co(III)][(eta5-C5H4COOH)2Co(III)]+[PF6]-, 2.1-[PF6]. The neutral zwitterion 2 behaves as a supramolecular crown ether: it encapsulates the alkali cations K+, Rb+ and Cs+ as well as the ammonium cation NH4+ in cages sustained by O-H...O and C-H...O hydrogen bonds to form co-crystalline salts of the type 2(2)-M[PF6] (M = K, Rb, Cs) and 2(2)-[NH4][PF6]. The deprotonated acid 3 has been characterised as its Cs+ salt, Cs+-3.3H2O.     

Syntheses,reactivity, and crystal structures of molybdenum complexes with pyridine-2-thionate (pyS)-containing ligands: crystal structures of [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2), exo-[Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-dppe)], [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)], and [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)

The doubly bridged pyridine-2-thionate (pyS) dimolybdenum complex [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2) (1) is accessible by the reaction of [Mo(eta(3)-C(3)H(5))(CO)(2)(CH(3)CN)(2)Br] with pySK in methanol at room temperature. Complex 1 reacts with piperidine in acetonitrile to give the complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(2)-pyS)(C(5)H(10)NH)] (2). Treatment of 1 with 1,10-phenanthroline (phen) results in the formation of complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(1)-pyS)(phen)] (3), in which the pyS ligand is coordinated to Mo through the sulfur atom. Four conformational isomers, endo,exo-complexes [Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-diphos)] (diphos = dppm, 4a-4d; dppe, 5a-5d), are accessible by the reactions of 1 with dppm and dppe in refluxing acetonitrile. Homonuclear shift-correlated 2-D (31)P((1)H)-(31)P((1)H) NMR experiments of the mixtures 4a-4d have been employed to elucidate the four stereoisomers. The reaction of 4 and pySK or [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)] (6) and O(2) affords allyl-displaced seven-coordinate bis(pyridine-2-thionate) complex [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)] (7). All of the complexes are identified by spectroscopic methods, and complexes 1, 5d, 6, and 7 are determined by single-crystal X-ray diffraction. Complexes 1 and 5d crystallize in the orthorhombic space groups Pbcn and Pbca with Z = 4 and 8, respectively, whereas 6 belongs to the monoclinic space group C2/c with Z = 8 and 7 belongs to the triclinic space group Ponemacr; with Z = 2. The cell dimensions are as follows: for 1, a = 8.3128(1) A, b = 16.1704(2) A, c = 16.6140(2) A; for 5d, a = 17.8309(10) A, b = 17.3324(10) A, c = 20.3716(11) A; for 6, a = 18.618(4) A, b = 16.062(2) A, c = 27.456(6) A, beta = 96.31(3) degrees; for 7, a = 9.1660(2) A, b = 12.0854(3) A, c = 15.9478(4) A, alpha = 78.4811(10) degrees, beta = 80.3894(10) degrees, gamma = 68.7089(11) degrees.     

Role of the transition metal in metallaborane chemistry. Reactivity of (Cp*ReH2)2B4H4 with BH3.thf, CO, and Co2(CO)8

The reaction of Cp*ReCl4, [Cp*ReCl3]2, or [Cp*ReCl2]2 (Cp* = eta 5-C5Me5) with LiBH4 leads to the formation of 7-skeletal-electron-pair (7-sep) (Cp*ReH2)2(B2H3)2 (1) together with Cp*ReH6. Compound 1 is metastable and eliminates H2 at room temperature to generate 6-sep (Cp*ReH2)2B4H4 (2). The reaction of 2 with BH3.thf produces 7-sep (Cp*Re)2B7H7, a hypoelectronic cluster characterized previously. Heating of 2 with 1 atm of CO leads to 6-sep (Cp*ReCO)(Cp*ReH2)B4H4 (3). Both 2 and 3 have the same bicapped Re2B2 tetrahedral cluster core structure. Monitoring the reaction of 2 with CO at room temperature by NMR reveals the formation of a 7-sep, metastable intermediate, (Cp*ReCO)(Cp*ReH2)(B2H3)2 (4), which converts to 3 on heating. An X-ray structure determination reveals two isomeric forms (4-cis and 4-trans) in the crystallographic asymmetric unit which differ in geometry relative to the disposition of the metal ancillary ligands with respect to the Re-Re bond. The presence of these isomers in solution is corroborated by the solution NMR data and the infrared spectrum. In both isomers, the metallaborane core consists of fused B2Re2 tetrahedra sharing the Re2 fragment. On the basis of similarities in electron count and spectroscopic data, 1 also possesses the same bitetrahedral structure. The reaction of 2 with CO2(CO)8 results in the formal replacement of the four rhenium hydrides with a 4-electron CO2(CO)5 fragment, thereby closing the open face in 2 to produce the 6-sep hypoelectronic cluster (Cp*Re)2CO2(CO)5B4H4 (5). These reaction outcomes are compared and contrasted with those previously observed for 5-sep (Cp*Cr2)2B4H8.     

2 + 2] cross coupling of benzene and tropylium ligands in reductively activated piano stool complexes of Mn,Cr, and W

We have established cation/anion coupling reactions between the tropylium ligand in [M(eta7-C7H7)(CO)3]+ (M = Cr, W) and the reductively activated eta4-benzene ligand in [Mn(eta4-C6H6)(CO)3]- (3-) to form [M(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3]; [Cr(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3] can be further reduced to [Cr(CO)3(mu2-eta5:eta4-C7H7-C6H6)Mn(CO)3]2-, in which the tropylium and benzene ligands have undergone a [2 + 2] cross coupling reaction.     

Preparations, structures, and electrochemical studies of aryldiazene complexes of rhenium: syntheses of the first heterobinuclear and heterotrinuclear derivatives with bis(diazene) or bis(diazenido) bridging ligands

The mono- and binuclear aryldiazene complexes [Re(C6H5N=NH)(CO)5-nPn]BY4 (1-5) and [(Re(CO)5-nPn)2-(mu-HN=NAr-ArN=NH)](BY4)2 (6-12) [P = P(OEt)3, PPh(OEt)2, PPh2OEt; n = 1-4; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-(2-CH3)C6H3-C6H3(2-CH3), 4,4'-C6H4-CH2-C6H4; Y = F, Ph) were prepared by reacting the hydride species ReH(CO)5-nPn with the appropriate mono- and bis(aryldiazonium) cations. These compounds, as well as other prepared compounds, were characterized spectroscopically (IR; 1H, 31P, 13C, and 15N NMR data), and 1a was also characterized by an X-ray crystal structure determination. [Re(C6H5N=NH)(CO)(P(OEt)3)4]BPh4 (1a) crystallizes in space group P1 with a = 15.380(5) A, b = 13.037(5) A, c = 16.649(5) A, alpha = 90.33(5) degrees, beta = 91.2(1) degrees, gamma = 89.71(9) degrees, and Z = 2. The "diazene-diazonium" complexes [M(CO)3P2(HN=NAr-ArN identical to N)](BF4)2 (13-15, 17) [M = Re, Mn; P = PPh2OEt, PPh2OMe, PPh3; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4] and [Re(CO)4(PPh2OEt)(4,4'-HN=NC6H4-C6H4N identical to N)](BF4)2 (16b) were synthesized by allowing the hydrides MH(CO)3P2 or ReH(CO)4P to react with equimolar amounts of bis(aryldiazonium) cations under appropriate conditions. Reactions of diazene-diazonium complexes 13-17 with the metal hydrides M2H2P'4 and M2'H(CO)5-nP"n afforded the heterobinuclear bis(aryldiazene) derivatives [M1(CO)3P2(mu-HN=NAr-ArN=NH)M2HP'4](BPh4)2 (ReFe, ReRu, ReOs, MnRu, MnOs) and [M1(CO)3P2(mu-HN=NAr-ArN=NH)M2'(CO)5-nP"n](BPh4)2 (ReMn, MnRe) [M1 = Re, Mn; M2 = Fe, Ru, Os; M2' = Mn, Re; P = PPh2OEt, PPh2OMe; P',P" = P(OEt)3, PPh(OEt)2; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4; n = 1, 2]. The heterotrinuclear complexes [Re(CO)3(PPh2OEt)2(mu-4,4'-HN=NC6H4-C6H4N=NH)M(P(OEt)3)4(mu-4,4'-HN=NC6H4- C6H4N=NH)Mn(CO)3(PPh2OEt)2](BPh4)4 (M = Ru, Os) (ReRuMn, ReOsMn) were obtained by reacting the heterobinuclear complexes ReRu and ReOs with the appropriate diazene-diazonium cations. The heterobinuclear complex with a bis(aryldiazenido) bridging ligand [Mn(CO)2(PPh2OEt)2(mu-4,4'-N2C6H4-C6H4N2)Fe(P(OEt)3)4]BPh4 (MnFe) was prepared by deprotonating the bis(aryldiazene) compound [Mn(CO)3(PPh2OEt)2(mu-4,4'-HN=NC6H4-C6H4N=NH)Fe(4- CH3C6H4CN)(P(OEt)3)4](BPh4)3. Finally, the binuclear compound [Re(CO)3(PPh2OEt)2(mu-4,4'-HN=NC6H4-C6H4N2)Fe(CO)2(P(OPh)3)2](BPh4)2 (ReFe) containing a diazene-diazenido bridging ligand was prepared by reacting [Re(CO)3(PPh2OEt)2(4,4'-HN=NC6H4-C6H4N identical to N)]+ with the FeH2(CO)2(P(OPh)3)2 hydride derivative. The electrochemical reduction of mono- and binuclear aryldiazene complexes of both rhenium (1-12) and the manganese, as well as heterobinuclear ReRu and MnRu complexes, was studied by means of cyclic voltammetry and digital simulation techniques. The electrochemical oxidation of the mono- and binuclear aryldiazenido compounds Mn(C6H5N2)(CO)2P2 and (Mn(CO)2P2)2(mu-4,4'-N2C6H4-C6H4N2) (P = PPh2OEt) was also examined. Electrochemical data show that, for binuclear compounds, the diazene bridging unit allows delocalization of electrons between the two different redox centers of the same molecule, whereas the two metal centers behave independently in the presence of the diazenido bridging unit.     

Heterometallic cluster complexes (RhMo, RhW) containing bridging 1,2-dicarba-closo-dodecaborane-1,2-dichalocogenolato ligands

The 16-electron half-sandwich rhodium complex [Cp*Rh{E2C2(B10H10)}] [Cp* = eta5-C5Me5, E = S (1a), Se (1b)] [Cp*Rh{E2C2(B10H10)} = eta5-pentamethylcyclopentadienyl[1,2-dicarba-closo-dodecaborane(12)-dichalcogenolato]rhodium] reacted with Mo(CO)3(py)3 in the presence of BF3.Et2O in THF solution to afford the {Cp*Rh[E2C2(B10H10)]}2Mo(CO)2 (E = S (3a); Se (3b)), {Cp*Rh[S2C2(B10H10)]}{Mo(CO)2[S2C2(B10H10)]} (4). The voluminous di-tert-butyl substituted Cp half-sandwich rhodium complex [Cp'Rh{E2C2(B10H10)}] [E = S (2a), Se (2b)] [CpRh{E2C2(B10H10)} = eta5-(1,3-di(tert-butyl)cyclopentadienyl-[1,2-dicarba-closo-dodecaborane(12)-dichalcogenolato]rhodium) reacted with W(CO)3(py)3 in the presence of BF3.Et2O in THF solution to give the {Cp'Rh[S2C2(B10H10)]}{W(CO)2[S2C2(B10H10)]} (5) and {Cp'Rh[Se2C2(B10H10)]}(mu-CO)[W(CO)3] (6), respectively. The complexes have been fully characterized by IR and NMR spectroscopy as well as by elemental analyses. The X-ray crystal structures of the complexes 3-6 are reported.     

Ammonolysis of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives

Ammonolyses of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives [Ti(eta5-C5Me5)X3] (X = NMe2, Me, Cl) have been carried out in solution to give polynuclear nitrido complexes. Reaction of the tris(dimethylamido) derivative [Ti(eta5-C5Me5)(NMe2)3] with excess of ammonia at 80-100 degrees C gives the cubane complex [[Ti(eta5-C5Me5)]4(mu3-N)4] (1). Treatment of the trimethyl derivative [Ti(eta5-C5Me5)Me3] with NH3 at room temperature leads to the trinuclear imido-nitrido complex [[Ti(eta/5-CsMes)(mu-NH)]3(mu3-N)] (2) via the intermediate [[Ti(eta5-C5Me5)Me]2(mu-NH)2] (3). The analogous reaction of [Ti(eta5-C5Me5)Me3] with 2,4,6-trimethylaniline (ArNH2) gives the dinuclear imido complex [[Ti(eta5-C5Me5)Me])2(mu-NAr)2] (4) which reacts with ammonia to afford [[Ti(eta5-C5Me5)(NH2)]2(mu-NAr)2] (5). Complex 2 has been used, by treatments with the tris(dimethylamido) derivatives [Ti(eta5-C5H5-nRn)(NMe2)3], as precursor of the cubane nitrido systems [[Ti4(eta5-C5Me5)3(eta5-C5H5-nRn)](mu3-N)4] [R = Me n = 5 (1), R = H n = 0 (6), R = SiMe3 n = 1 (7), R = Me n = 1 (8)] via dimethylamine elimination. Reaction of [Ti(eta5-C5Me5)Cl3] or [Ti(eta5-C5Me5)(NMe2)Cl2] with excess of ammonia at room temperature gives the dinuclear complex [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) where an intramolecular hydrogen bonding and a nonlineal nitrido ligand bridge the "Ti(eta5-C5Me5)Cl(NH3)" and "Ti(eta5-C5Me5)Cl2" moieties. The molecular structures of [[Ti(eta5-C5Me5)Me]2 (mu-NAr)2] (4) and [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) have been determined by X-ray crystallographic studies. Density functional theory calculations also have been conducted on complex 9 to confirm the existence of an intramolecular N-H...Cl hydrogen bond and to evaluate different aspects of its molecular disposition.     

Migratory insertion of [B(C6F5)2] into C-H bonds: CO promoted transfer of the boryl fragment

The reaction of (eta(5)-C5H5)Fe(CO)2B(C6F5)2 with CO has been shown to proceed via ligand substitution at the metal with accompanying transfer of the boryl fragment (via C-H insertion) to the Cp ring, thereby generating the zwitterion [eta(5)-C5H4B(C6F5)2H]Fe(CO)3 in quantitative yield.     

Phosphaallyl complexes of Ru(II) derived from dicyclohexylvinylphosphine (DCVP)

The complexes [(eta5-RC5H4)Ru(CH3CN)3]PF6(R = H, CH3) react with DCVP (DCVP = Cy2PCH=CH2) at room temperature to produce the phosphaallyl complexes [(eta5-C5H5)Ru(eta1-DCVP)(eta3-DCVP)]PF6 and [(eta5-MeC5H4)Ru(eta1-DCVP)(eta3-DCVP)]PF6. Both compounds react with a variety of two-electron donor ligands displacing the coordinated vinyl moiety. In contrast, we failed to prepare the phosphaallyl complexes [(eta5-C5Me5)Ru(eta1-DCVP)(eta3-DCVP)]PF6, [(eta5-MeC5H4)Ru(CO)(eta3-DCVP)]PF6 and [(eta5-C5Me5)Ru(CO)(eta3-DPVP)]PF6(DPVP = Ph2PCH=CH2).The compounds [(eta5-MeC5H4)Ru(CO)(CH3CN)(DPVP)]PF6 and [(eta5-C5Me5)Ru(CO)(CH3CN)(DPVP)]PF6 react with DMPP (3,4-dimethyl-1-phenylphosphole) to undergo [4 + 2] Diels-Alder cycloaddition reactions at elevated temperature. Attempts at ruthenium catalyzed hydration of phenylacetylene produced neither acetophenone nor phenylacetaldehyde but rather dimers and trimers of phenylacetylene. The structures of the complexes described herein have been deduced from elemental analyses, infrared spectroscopy, 1H, 13C{1H}, 31P{1H} NMR spectroscopy and in several cases by X-ray crystallography.     

Structural isomers of aryl-substituted eta(3)-propargyl complexes: eta(2)-1-Metalla(methylene)cyclopropene and eta(3)-benzyl complexes

Hydride abstraction from C(5)Me(5)(CO)(2)Re(eta(2)-PhC triple bond CCH(2)Ph) (1) gave a 3:1 mixture of eta(3)-propargyl complex [C(5)Me(5)(CO)(2)Re(eta(3)-PhCH-C triple bond CPh)][BF(4)] (5) and eta(2)-1-metalla(methylene)cyclopropene complex [C(5)Me(5)(CO)(2)Re(eta(2)-PhC-C=CHPh)][BF(4)] (6). Observation of the eta(2)-isomer requires 1,3-diaryl substitution and is favored by electron-donating substituents on the C(3)-aryl ring. Interconversion of eta(3)-propargyl and eta(2)-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp (1)H NMR resonances at about -50 degrees C. Protonation of the alkynyl carbene complex C(5)Me(5)(CO)(2)Re=C(Ph)C triple bond CPh (22) gave a third isomer, the eta(3)-benzyl complex [C(5)Me(5)(CO)(2)Re[eta(3)(alpha,1,2)-endo,syn-C(6)H(5)CH(C triple bond CC(6)H(5))]][BF(4)] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium, there is no equilibration of the eta(3)-benzyl isomer 23 with 5 and 6.     

Various forms of linear dipyridyls in discrete rectangles, dinuclear rods, and one-dimensional networks containing (eta5-pentamethylcyclopentadienyl)rhodium(III)

[Cp*Rh(eta1-NO3)(eta2-NO3)] (1) reacted with pyrazine (pyz) to give a dinuclear complex [Cp*Rh(eta1-NO3)(mu-pyz)(0.5)]2.CH2Cl2(3.CH2Cl2). Tetranuclear rectangles of the type [Cp*Rh(eta1,mu-X)(mu-L)(0.5)]4(OTf)4(4a: X = N3, L = bpy; 4b: X = N3, L = bpe; 4c: X = NCO, L = bpy) were prepared from [Cp*Rh(H2O)3](OTf)2 (2), a pseudo-halide (Me3SiN3 or Me3SiNCO), and a linear dipyridyl [4,4'-bipyridine (bpy) or trans-1,2-bis(4-pyridyl)ethylene (bpe)] by self-assembly through one-pot synthesis at room temperature. Treating complex with NH4SCN and dipyridyl led to the formation of dinuclear rods, [Cp*Rh(eta1-SCN)3]2(LH2) (5a: L = bpy; 5b: L = bpe), in which two Cp*Rh(eta1-SCN)3 units are connected by the diprotonated dipyridyl (LH2(2+)) through N(+)-H...N hydrogen bonds. Reactions of complex 2 with 1-(trimethylsilyl)imidazole (TMSIm) and dipyridyl (bpy or bpe) also produced another family of dinuclear rods [Cp*Rh(ImH)3]2.L (6a: L = bpy; 6b: L = bpe). Treating 1 and 2 with TMSIm and NH4SCN (in the absence of dipyridyl) generated a 1-D chain [Cp*Rh(ImH)3](NO3)2 (7) and a 1-D helix [Cp*Rh(eta1-SCN)2(eta1-SHCN)].H2O (8.H2O), respectively. The structures of complexes 3.CH2Cl2, 4a.H2O, 4c.2H2O, 5b, 6a, 7 and 8.H2O were determined by X-ray diffraction.     

Unsaturated binuclear cyclopentadienylrhenium carbonyl derivatives: metal-metal multiple bonds and agostic hydrogen atoms

The cyclopentadienylrhenium carbonyls Cp 2Re 2(CO) n (Cp = eta (5)-C 5H 5; n = 5, 4, 3, 2) have been studied by density functional theory. The global minima for the Cp 2Re 2(CO) n ( n = 5, 4, 3, 2) derivatives are predicted to be the singly bridged structure Cp 2Re 2(CO) 4(mu-CO) with a formal Re-Re single bond; the doubly semibridged structure Cp 2Re 2(CO) 4 with a formal ReRe double bond; the triply bridged structure Cp 2Re 2(mu-CO) 3 with a formal ReRe triple bond; and the doubly bridged structure Cp 2Re 2(mu-CO) 2, respectively. The first three of these predicted structures have been realized experimentally in the stable compounds (eta (5)-C 5H 5) 2Re 2(CO) 4(mu-CO), (eta (5)-Me 5C 5) 2Re 2(CO) 4 and (eta (5)-Me 5C 5) 2Re 2(mu-CO) 3. In addition, structures of the type Cp 2Re-Re(CO) n with both rings bonded only to one metal and unknown in manganese chemistry are also found for rhenium but at energies significantly above the global minima. The unsaturated Cp 2Re-Re(CO) n structures ( n = 4, 3, 2) have agostic Cp hydrogen atoms forming C-H-Re bridges to the unsaturated Re(CO) n group with a Re-H distance as short as 2.04 A.