M. Esther García

Activation of H-H and H-O bonds at phosphorus with diiron complexes bearing pyramidal phosphinidene ligands.

The complex [Fe(2)Cp(2)(μ-PMes*)(μ-CO)(CO)(2)] (Mes* = 2,4,6-C(6)H(2)(t)Bu(3)), which in the solid state displays a pyramidal phosphinidene bridge, reacted at room temperature with H(2) (ca. 4 atm) to give the known phosphine complex [Fe(2)Cp(2)(μ-CO)(2)(CO)(PH(2)Mes*)] as the major product, along with small amounts of other byproducts arising from the thermal degradation of the starting material, such as the phosphindole complex [Fe(2)Cp(2)(μ-CO)(2)(CO){PH(CH(2)CMe(2))C(6)H(2)(t)Bu(2)}], the dimer [Fe(2)Cp(2)(CO)(4)], and free phosphine PH(2)Mes*. During the course of the reaction, trace amounts of the mononuclear phosphide complex [FeCp(CO)(2)(PHMes*)] were also detected, a compound later found to be the major product in the carbonylation of the parent phosphinidene complex, with this reaction also yielding the dimer [Fe(2)Cp(2)(CO)(4)] and the known diphosphene Mes*P═PMes*. The outcome of the carbonylation reactions of the title complex could be rationalized by assuming the formation of an unstable tetracarbonyl intermediate [Fe(2)Cp(2)(μ-PMes*)(CO)(4)] (undetected) that would undergo a fast homolytic cleavage of a Fe-P bond, this being followed by subsequent evolution of the radical species so generated through either dimerization or reaction with trace amounts of water present in the reaction media. A more rational synthetic procedure for the phosphide complex was accomplished through deprotonation of the phosphine compound [FeCp(CO)(2)(PH(2)Mes*)](BF(4)) with Na(OH), the latter in turn being prepared via oxidation of [Fe(2)Cp(2)(CO)(4)] with [FeCp(2)](BF(4)) in the presence of PH(2)Mes*. To account for the hydrogenation of the parent phosphinidene complex it was assumed that, in solution, small amounts of an isomer displaying a terminal phosphinidene ligand would coexist with the more stable bridged form, a proposal supported by density functional theory (DFT) calculations of both isomers, with the latter also revealing that the frontier orbitals of the terminal isomer (only 5.7 kJ mol(-1) above of the bridged isomer, in toluene solution) have the right shapes to interact with the H(2) molecule. In contrast to the above behavior, the cyclohexylphosphinidene complex [Fe(2)Cp(2)(μ-PCy)(μ-CO)(CO)(2)] failed to react with H(2) under conditions comparable to those of its PMes* analogue. Instead, it slowly reacted with HOR (R = H, Et) to give the corresponding phosphinous acid (or ethyl phosphinite) complexes [Fe(2)Cp(2)(μ-CO)(2)(CO){PH(OR)Mes*}], a behavior not observed for the PMes* complex. The presence of BEt(3) increased significantly the rate of the above reaction, thus pointing to a pathway initiated with deprotonation of an O-H bond of the reagent by the basic P center of the phosphinidene complex, this being followed by the nucleophilic attack of the OR(-) anion at the P site of the transient cationic phosphide thus formed. The solid-state structure of the cis isomer of the ethanol derivative was determined through a single crystal X-ray diffraction study (Fe-Fe = 2.5112(8) Å, Fe-P = 2.149(1) Å).

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].

Proton induced P–H and Mo–H bond activation at the phosphide bridged dimolybdenum complexes [Mo2Cp2(µ-H)(µ-PHR)(CO)4](R = Cy, 2,4,6-C6H2R′3; R′= H, Me, tBu)

The new hydride complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4] having bulky substituents (R = 2,4,6-C(6)H2tBu3= Mes*, R = 2,4,6-C6H2Me3= Mes) have been prepared in good yield by addition of Li[PHR] to the triply bonded [Mo2Cp2(CO)4] and further protonation of the resulting anionic phosphide complex [Mo2Cp2(mu-PHR)(CO)4]-. Protonation of the Mes* compound with either [H(OEt2)2][B{3,5-C6H3(CF3)2}4] or HBF4.OEt2 gives the cationic phosphinidene complex [Mo2Cp2(mu-H)(mu-PMes*)(CO)4]+ in high yield. In contrast, protonation of the analogous hydride compounds with Mes or Cy substituents on phosphorus give the corresponding unsaturated tetracarbonyls [Mo2Cp2(mu-PHR)(CO)4]+, which are unstable at room temperature and display a cis geometry. Decomposition of the latter give the electron-precise pentacarbonyls [Mo2Cp2(mu-PHR)(mu-CO)(CO)4]+, also displaying a cis arrangement of the metal fragments. In the presence of BF4- as external anion, fluoride abstraction competes with carbonylation to yield the neutral fluorophosphide hydrides [Mo2Cp2(mu-H)(mu-PFR)(CO)4]. Similar results were obtained in the protonation reactions of the hydride compounds having a Ph substituent on phosphorus. In that case, using HCl as protonation reagent gave the chloro-complex [Mo2ClCp2(mu-PHPh)(CO)4] in good yield. The structures and dynamic behaviour of the new compounds are analyzed on the basis of solution IR and 1H, 31P, 19F and 13C NMR data as well as the X-ray studies carried out on [Mo2Cp2(mu-H)(mu-PHMes)(CO)4](cis isomer), [Mo2Cp2(mu-H)(mu-PFMes)(CO)4](trans isomer), [Mo2Cp2(mu-PHCy)(mu-CO)(CO)4](BF4) and [Mo2ClCp2(mu-PHPh)(CO)4].

Mild P4 activation to give an anionic diphosphorus complex with a dual binding ability at a single P site.

The anion [Mo(2)Cp(2)(μ-PCy(2))(μ-CO)(2)](-) (1; Li(+) salt) reacts at 290 K with P(4) to give the diphosphorus-bridged complex [Mo(2)Cp(2)(μ-PCy(2))(CO)(2)(μ-κ(2):κ(2)-P(2))](-) (2). The latter reacts with MeI and ClSnPh(3) through a single P atom to give respectively diphosphenyl [Mo(2)Cp(2)(μ-PCy(2))(CO)(2)(μ-κ(2):κ(2)-P(2)Me)] (3) and stannyl [Mo(2)Cp(2)(μ-PCy(2))(CO)(2){μ-κ(2):κ(2)-P(2)(SnPh(3))}] (4) derivatives, with the P-P-Sn angle in 4 being unexpectedly acute [80.3(1)°]. According to density functional theory calculations, this novel nucleophilic behavior of 1 is derived from its anionic nature, thus enabling the P(2) ligand to act in a π-donor-like fashion.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 56. Synthesis of iron–molybdenum compounds; crystal structures of [FeMo(µ-CR)(CO)6(η-C5H5)] and [FeMo2(µ3-RC2R)(CO)6(η-C5H5)2](R = C6H4Me-4)

Equivalent amounts of [Fe2(CO)9] and [Mo(CR)(CO)2(η-C5H5)](R = C6H4Me-4) react in Et2O at room temperature to give the dimetal complex [FeMo(µ-CR)(CO)6(η-C5H5)], the structure of which has been established by X-ray diffraction. Four CO groups are terminally bound to the iron atom and two to the molybdenum, with the latter also carrying the η-C5H5 ligand. The dimensions of the dimetallacyclopropene ring are Fe–Mo 2.823(1), µ-C–Fe 2.008(5), and µ-C–Mo 1.921(5)A. Excess of [Fe2(CO)9] and [Mo(CR)(CO)2(η-C5H5)] react at room temperature in Et2O to give the trimetal compound [Fe2Mo(µ3-CR)(µ-CO)(CO)8(η-C5H5)]. In contrast, reaction between one equivalent of nonacarbonyldi-iron and two equivalents of the tolylmethylidynemolybdenum compound affords the 46-valence-electron irondimolybdenum cluster [FeMo2(µ3-RC2R)(CO)6(η-C5H5)2], the structure of which was confirmed by an X-ray diffraction study. The alkyne ligand adopts a µ3-(η2-⊥) bonding mode towards the metal triangle [Mo–Mo 2.764(1), Fe–Mo 2.732(1) and 2.761(1)A], and one carbonyl ligand semi-bridges the molybdenum–molybdenum bond [Mo–C–O 162.5(3)°]. Reaction between one equivalent of the bis(cyclo-octene) iron complex [Fe(CO)3(η-C8H14)2] and two equivalents of [Mo(CR)(CO)2(η-C5H5)], in light petroleum at –40 °C, affords the thermally labile heptacarbonylirondimolybdenum compound [FeMo2(µ3-RC2R)(CO)7(η-C5H5)2]. The latter readily releases a molecule of CO to give [FeMo2(µ3-RC2R)(CO)6(η-C5H5)2], but this process is reversed at –20 °C. The spectroscopic properties of the new compounds are reported and discussed.

Chemistry of the Oxophosphinidene Ligand. 1. Electronic Structure of the Anionic Complexes [MCp{P(O)R*}(CO)2]- (M = Mo, W; R* = 2,4,6-C6H2tBu3) and Their Reactions with H+ and C-Based Electrophiles

The anionic phosphide-bridged complexes (H-DBU)[M(2)Cp(2)(μ-PHR*)(CO)(4)] (M = Mo, W; R* = 2,4,6-C(6)H(2)(t)Bu(3); Cp = η(5)-C(5)H(5), DBU = 1,8-diazabicyclo [5.4.0] undec-7-ene) react with molecular oxygen to give the corresponding oxophosphinidene complexes (H-DBU)[MCp{P(O)R*}(CO)(2)] as major products (Mo-P = 2.239(1) Å for the Mo complex). The latter anionic complexes are protonated by HBF(4)·OEt(2) to give the hydroxyphosphide derivatives [MCp{P(OH)R*}(CO)(2)]. In the presence of excess acid, the molybdenum complex yields the fluorophosphide complex [MoCp(PFR*)(CO)(2)] (Mo-P = 2.204(1) Å), while the tungsten compound reacts with excess HCl to give an unstable chlorophosphine complex [WCpCl(PHClR*)(CO)(2)] which is rapidly hydrolyzed to give [WCpCl{PH(OH)R*}(CO)(2)], having a complexed arylphosphinous acid (Mo-P = 2.460(2) Å). The molybdenum anion reacts with strong C-based electrophiles such as [Me(3)O]BF(4), Et(2)SO(4), C(2)H(3)C(O)Cl, and PhC(O)Cl to give the corresponding alkoxyphosphide derivatives [MoCp{P(OR)R*}(CO)(2)] (R = Me, Et, COC(2)H(3), COPh; Mo-P = 2.197(2) Å for the benzoyl compound), as a result of the attack of the electrophile at the O atom of the oxophosphinidene ligand. In contrast, the reactions with milder alkylating reagents such as the alkyl halides MeI, EtI, C(3)H(5)Br, and C(3)H(3)Br give selectively the corresponding κ(2)-phosphinite complexes [MoCp{κ(2)-OP(R)R*}(CO)(2)] [R = Me, Et, C(3)H(5), C(3)H(3); Mo-P = 2.3733(5) Å for the allyl compound] as a result of the attack of the electrophile at the P atom of the oxophosphinidene ligand. According to density functional theory (DFT) calculations, the oxygen atom of the phosphinidene ligand bears the highest negative charge in the molybdenum anion, while the highest occupied molecular orbital (HOMO) of this complex has substantial Mo-P π bonding character. Thus, it is concluded that the phosphinite complexes are formed under conditions of orbital control, while charge-controlled reactions tend to give alkoxyphosphide derivatives.

Homonuclear PdII and PtII and heteronuclear PdII-AuI and PtII-AuI complexes of a tripod triphosphine ligand: synthesis, characterization and reactions with molecules of biological relevance

Complexes of the type Pd(tripod)X2 [tripod = MeC(CH2PPh2)3; X = Cl (1), Br (2), I (3)] and Pt(tripod)X2 [X = Cl (4), Br (5), I (6)] have been synthesized. In these complexes tripod acts as a bidentate chelating ligand. The uncoordinated phosphorus atom can bind to AuI to form the bimetallic complexes PdAu(tripod)X3 [X = Cl (7), Br (8), I (9)] and PtAu(tripod)X3 [X = Cl (10), Br (11), I (12)]. Complexes (1)–(12) have been characterized by microanalysis, f.a.b. mass spectrometry, i.r. spectroscopy, 31P and 195Pt n.m.r. spectroscopies, and conductivity measurements. The structures of complexes (1), (4) and (11), as well as that of the unusual complex Cl2Pt(tripod)AuBr0.5Cl0.5 (13), isolated from reaction of Pt(tripod)Br2 (5), and [Au(thiodiglycol)Cl], have been determined. All complexes show square-planar geometry for PdII or PtII and linear geometry for AuI. The X-ray crystal structure of (1) showed partial oxidation of the dangling phosphorus of the ligand in 50% of the molecule distributed randomly over the lattice. Reactions of complex (4), Pt(tripod)Cl2, with the tripeptide glutathione (GSH) showed the formation of [Pt2(tripod)2(GS-µ–S)2]2+ (15a). No reaction with N-acetyl-L-methionine (AcMet) or guanosine 5´-monophosphate (5´-GMP) was observed. Reactions of [Pt(tripod–O)(ONO2)2] (14) with GSH resulted in the formation of [Pt2(tripod–O)2(GS-µ-S)2]2+ (15b). Displacement of the S-containing molecules by 5´-GMP in the presence of AuI, via Pt–S bond cleavage, was observed for complex (15b). PtAu(tripod)Cl3 (10) reacted with GSH, with initial attack on the AuI centre.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 64. Addition of methylene groups to iron–molybdenum complexes; crystal structures of [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)] and [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)]

The reaction between [FeMo(µ-CC6H4Me-4)(CO)6(η-C5H5)] and CH2N2 in diethyl ether at ambient temperatures affords the complex [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)], whereas if the reaction is carried out at ca.–40 °C the product is [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)]. Both species correspond to the addition of two CH2 fragments to the precursor, and their molecular structures have been established by single-crystal X-ray diffraction studies. In [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)5(η-C5H5)] the Fe–Mo bond [2.717(1)A] is asymmetrically bridged by the CH2 group [µ-C–Fe 2.016(3), µ-C–Mo 2.239(3)A], and the C(C6H4Me-4)CH2 fragment is σ-bonded to molybdenum [C–Mo 2.209(2)A] and η-co-ordinated to iron [C–Fe 2.055(2) and 2.127(3)A]. The molecule of [FeMo{µ-C(C6H4Me-4)C(OMe)C(H)}(CO)5(η-C5H5)] has an Fe–Mo bond [2.704(1)A] transversely bridged by a C(C6H4Me-4)C(OMe)C(H) fragment, with the latter η3-co-ordinated to the iron and with the two end carbons of the C3 chain σ-bonded to the molybdenum. Reactions between the complexes [FeMo(µ-CC6H4Me-4)(CO)n( PMe3)(η-C5H5)](n= 4 and 5) and CH2N2 have also been investigated, and the compounds [FeMo(µ-CH2){µ-σ:η-C(C6H4Me-4)CH2}(CO)4(PMe3)(η-C5H5)] and [FeMo{µ-C(C6H4Me-4)C(OH)C(H)}(CO)4(PMe3)(η-C5H5)] thereby obtained. The 1H and 13C-{1H} n.m.r. spectra of the new compounds are reported and discussed, and pathways proposed for their formation.

Reactivity of the anionic diphosphorus complex [Mo2Cp2(μ-PCy2)(CO)2(μ-κ2:κ2-P2)]- toward ER3X electrophiles (E = C to Pb): insights into the multisite donor ability and dynamics of the P2 ligand.

The Li(+) salt of the unsaturated anion [Mo(2)Cp(2)(μ-PCy(2))(μ-CO)(2)](-) reacted with P(4) in tetrahydrofuran at room temperature to give the title complex. This fluxional anion reacted with MeI and ClCH(2)Ph to give the diphosphenyl complexes [Mo(2)Cp(2)(μ-κ(2):κ(2)-P(2)CH(2)R)(μ-PCy(2))(CO)(2)] (R = H, Ph), with the incoming electrophile being attached at the basal P atom of the Mo(2)P(2) tetrahedron via the lone electron pair (P-P-CH(3) = 122.8(1)(o)). In contrast, reactions with ClER(3) (ER(3) = GePh(3), SnPh(3), PbMe(3), PbPh(3)) gave neutral complexes [Mo(2)Cp(2)(μ-κ(2):κ(2)-P(2)ER(3))(μ-PCy(2))(CO)(2)] having the incoming electrophile attached at the basal P atom but defining an acute P-P-E angle close to 90° with elongated P-P lengths of ca. 2.20 Å. These complexes undergo an easy fluxional process involving an exchange of the ER(3) group between the P atoms that could be properly modeled through DFT calculations, and some of them displayed minor isomers in solution. Their structure could be rationalized as derived from the interaction of the electrophile with high-energy orbitals of the anion having both σ(Mo-P) and π(P-P) bonding character. Reaction with BrSiMe(3) gave instead the agostic phosphenyl complex [Mo(2)Cp(2)(μ-κ(2):κ(1),η(2)-HP(2))(μ-PCy(2))(CO)(2)], formally derived from the attachment of a proton to a basal Mo-P edge of the anion (computed length 2.810 Å) and displaying an unusually low P-H coupling of 4 Hz. A similar structure, with the agostic H atom replaced with SnH(3), was found to be a satisfactory model for the minor isomer of the tin compound and represents a third and unprecedented coordination mode of the diphosphorus ligand. The agostic complex undergoes a fluxional process involving the intermediacy of the nonagostic isomer [Mo(2)Cp(2)(μ-κ(2):κ(2)-P(2)H)(μ-PCy(2))(CO)(2)], which was computed to display a geometry comparable to the major isomers of the ER(3) compounds (P-P = 2.183 Å; P-P-H = 81.7°).

Reactions of the Unsaturated Complex [Mo2(η5-C5H5)2(μ-PEt2)2(CO)2] with [Au(PR3)]+ Cations: Kinetic Preference of the Mo-P Bonds as the Site of Attack of the Gold(I) Electrophile

The title complex reacts with [Au(PR(3))](+) cations (PF(6)(-) salts, R = p-tol, Me) in dichloromethane solutions to give first the corresponding agostic-like products [AuMo(2)Cp(2)(mu-PEt(2))(mu(3)-PEt(2))(CO)(2)(PR(3))]PF(6), which then partially rearrange to reach an equilibrium with the hydride-like isomers [AuMo(2)Cp(2)(mu-PEt(2))(2)(CO)(2)(PR(3))]PF(6), the latter being characterized through an X-ray study (R = p-tol, Mo-Mo = 2.8244(2) A). These unsaturated complexes react smoothly with CO (1 atm) to give the corresponding electron-precise derivatives [AuMo(2)Cp(2)(mu-PEt(2))(2)(CO)(3)(PR(3))](+) (Mo-Mo = 3.0438(6) A when R = Me), this implying the rearrangement of the mu(3)-PEt(2) ligand to a more common mu(2)-coordination mode. Density functional theory (DFT) calculations on the dimolybdenum complexes [Mo(2)Cp(2)(mu-PR(2))(2)(CO)(2)] (R = Cy, Et) reveal the presence of a framework M-P bonding orbital high in energy and with the right shape to act as a donor to H(+) and [Au(PR(3))](+) cations, thus explaining the formation of agostic and agostic-like products respectively in these reactions. The unusually high energy of this donor orbital can be related to the close approach of the metal centers in these unsaturated molecules. The carbyne complex [Mo(2)Cp(2)(mu-COMe)(mu-PCy(2))(CO)(2)] reacts with [Au{P(p-tol)(3)}](+) to give the tricarbonyl [AuMo(2)Cp(2)(mu-COMe)(mu-PCy(2))(CO)(3){P(p-tol)(3)}](+) (Mo-Mo = 2.986(1) A), a process most likely initiated by the binding of the gold cation to one of the Mo-P bonds in the carbyne complex.