P2 addition to terminal phosphide M[triple bond]P triple bonds: a rational synthesis of cyclo-P3 complexes

The diphosphaazide complex (Mes*NPP)Nb(N[Np]Ar)3 (Mes* = 2,4,6-tri-tert-butylphenyl, Np = neopentyl, Ar = 3,5-Me2C6H3), 1, has previously been reported to lose the P2 unit upon gentle heating, to form (Mes*N)Nb(N[Np]Ar)3, 2. The first-order activation parameters for this process have been estimated here using an Eyring analysis to have the values Delta H(double dagger) = 19.6(2) kcal/mol and Delta S(double dagger) = -14.2(5) eu. The eliminated P2 unit can be transferred to the terminal phosphide complexes P[triple bond]M(N[(i)Pr]Ar)3, 3-M (M = Mo, W), and [P[triple bond]Nb(N[Np]Ar)3](-), 3-Nb, to give the cyclo-P3 complexes (P3)M(N[(i)Pr]Ar)3 and [(P3)Nb(N[Np]Ar)3](-). These reactions represent the formal addition of a P[triple bond]P triple bond across a M[triple bond]P triple bond and are the first efficient transfers of the P2 unit to substrates present in stoichiometric quantities. The related complex (OC)5W(Mes*NPP)Nb(N[Np]Ar)3, 1-W(CO)5, was used to transfer the (P2)W(CO)5 unit in an analogous manner to the substrates 3-M (M = Mo, W, Nb) as well as to [(OC)5WP[triple bond]Nb(N[Np]Ar)3](-). The rate constants for the fragmentation of 1 and 1-W(CO)5 were unchanged in the presence of the terminal phosphide 3-Mo, supporting the hypothesis that molecular P2 and (P2)W(CO)5, respectively, are reactive intermediates. In a reaction related to the combination of P[triple bond]P and M[triple bond]P triple bonds, the phosphaalkyne AdC[triple bond]P (Ad = 1-adamantyl) was observed to react with 3-Mo to generate the cyclo-CP2 complex (AdCP2)Mo(N[(i)Pr]Ar)3. Reactions of the electrophiles Ph3SnCl, Mes*NPCl, and AdC(O)Cl with the anionic, nucleophilic complexes [(OC)5W(P3)Nb(N[Np]Ar)3](-) and [{(OC)5W}2(P3)Nb(N[Np]Ar)3](-) yielded coordinated eta(2)-triphosphirene ligands. The Mes*NPW(CO)5 group of one such product engages in a fluxional ring-migration process, according to NMR spectroscopic data. The structures of (OC)5W(P3)W(N[(i)Pr]Ar)3, [(Et2O)Na][{(OC)5W}2(P3)Nb(N[Np]Ar)3], (AdCP2)Mo(N[(i)Pr]Ar)3, (OC)5W(Ph3SnP3)Nb(N[Np]Ar)3, Mes*NP(W(CO)5)P3Nb(N[Np]Ar)3, and {(OC)5W}2AdC(O)P3Nb(N[Np]Ar)3, as determined by X-ray crystallography, are discussed in detail.     

Different coordination modes of 2-(diphenylphosphino)azobenzenes in complexation with hard and soft metals

Control of coordination modes of a ligand in metal complexes is significant because the coordination modes influence catalytic properties of transition metal catalysts. Reactions of 2-diphenylphosphinoazobenzenes, which are in equilibrium with the inner phosphonium salts, with ZnCl(2), W(CO)(5)(THF), and PtCl(2)(cod) gave three different coordination types of metal complexes with distinctive UV-vis absorptions. All the complexes were characterized by X-ray crystallographic analyses. In the zinc and tungsten complexes, the source molecule functions as an amide ligand and a phosphine ligand, respectively. In the platinum complex, the phosphorus molecule works as a tridentate ligand with formation of a carbon-platinum bond.     

Synthesis and structural characterization of configurational isomers of tungsten-palladium complexes with bridging diphenyl(dithioalkoxycarbonyl)phosphine as a ligand and phosphine transfer from tungsten to palladium

Treatment of the complex [W(CO)5[PPh2(CS2Me)]] (2) with [Pd(PPh3)4] (1) affords binuclear complexes such as anti-[(Ph3P)2Pd[mu-eta 1,eta 2-(CS2Me)PPh2]W(CO)5] (3), syn-[(Ph3P)2Pd[mu-eta 1,eta 2-(CS2Me)PPh2]W(CO)5] (4), and trans-[W(CO)4(PPh3)2] (5). In 3 and 4, respectively, the W and Pd atoms are in anti and syn configurations with respect to the P-CS2 bond of the diphenyl(dithiomethoxycarbonyl)phosphine ligand, PPh2(CS2Me). Complex 3 undergoes extensive rearrangement in CHCl3 at room temperature by transfer of a PPh3 ligand from Pd to W, eliminating [W(CO)5(PPh3)] (7), while the PPh2CS2Me ligand transfers from W to Pd to give [[(Ph3P)Pd[mu-eta 1,eta 2-(CS2Me)PPh2]]2] (6). In complex 6, the [Pd(PPh3)] fragments are held together by two bridging PPh2(CS2Me) ligands. Each PPh2(CS2Me) ligand is pi-bonded to one Pd atom through the C=S linkage and sigma-bonded to the other Pd through the phosphorus atom, resulting in a six-membered ring. Treatment of Pd(PPh3)4 with [W(CO)5[PPh2[CS2(CH2)nCN]]] (n = 1, 8a; n = 2, 8b) in CH2Cl2 affords syn-[(Ph3P)2Pd[mu-eta 1,eta 2-[CS2(CH2)nCN]PPh2]W(CO)5] (n = 1, 9a; n = 2, 9b). Similar configurational products syn-[(Ph3P)2Pd[mu-eta 1,eta 2-(CS2R)PPh2]W(CO)5] (R = C2H5, C3H5, C2H4OH, C3H6CN, 11a-d) are synthesized by the reaction of Pd(PPh3)4 with [W(CO)5[PPh2(CS2R)]] (R = C2H5, C3H5, C2H4OH, C3H6CN, 10a-d). Although complexes 11a-d have the same configuration as 9a,b, the SR group is oriented away from Pd in the former and near Pd in the latter. In these complexes, the diphenyl(dithioalkoxycarbonyl)phosphine ligand is bound to the two metals through the C=S pi-bonding and to phosphorus through the sigma-bonding. All of the complexes are identified by spectroscopic methods, and the structures of complexes 3, 6, 9a, and 11d are determined by single-crystal X-ray diffraction. Complexes 3, 9, and 11d crystallize in the triclinic space group P1 with Z = 2, whereas 6 belongs to the monoclinic space group P2/c with Z = 4. The cell dimensions are as follows: for 3, a = 10.920(3) A, b = 14.707(5) A, c = 16.654(5) A, alpha = 99.98(3) degrees, beta = 93.75(3) degrees, gamma = 99.44(3) degrees; for 6, a = 15.106(3) A, b = 9.848(3) A, c = 20.528(4) A, beta = 104.85(2) degrees; for 9a, a = 11.125(3) A, b = 14.089(4) A, c = 17.947(7) A, alpha = 80.13(3) degrees, beta = 80.39(3) degrees, gamma = 89.76(2) degrees; for 11d, a = 11.692(3) A, b = 13.602(9) A, c = 18.471(10) A, alpha = 81.29(5) degrees, beta = 80.88(3) degrees, gamma = 88.82(1) degrees.     

Synthesis and characterisation of triselenocarbonate [CSe3]2- complexes

[Pt(CSe3)(PR3)2] (PR3= PMe3, PMe2Ph, PPh3, P(p-tol)3, 1/2 dppp, 1/2 dppf) were all obtained by the reaction of the appropriate metal halide containing complex with carbon diselenide in liquid ammonia. Similar reaction with [Pt(Cl)2(dppe)] gave a mixture of triselenocarbonate and perselenocarbonate complexes. [{Pt(mu-CSe3)(PEt3)}4] was formed when the analogous procedure was carried out using [Pt(Cl)2(PEt3)2]. Further reaction of [Pt(CSe3)(PMe2Ph)2] with [M(CO)6] (M = Cr, W, Mo) yielded bimetallic species of the type [Pt(PMe2Ph)2(CSe3)M(CO)5] (M = Cr, W, Mo). The dimeric triselenocarbonate complexes [M{(CSe3)(eta5-C5Me5)}2] (M = Rh, Ir) and [{M(CSe3)(eta6-p-MeC6H4(i)Pr)}2] (M = Ru, Os) have been synthesised from the appropriate transition metal dimer starting material. The triselenocarbonate ligand is Se,Se' bidentate in the monomeric complexes. In the tetrameric structure the exocyclic selenium atoms link the four platinum centres together.     

Mixed-metal cluster chemistry. 28. Core enlargement of tungsten-iridium clusters with alkynyl, ethyndiyl, and butadiyndiyl reagents

Reaction of [WIr3(mu-CO)3(CO)8(eta-C5Me5)] (1c) with [W(C[triple bond]CPh)(CO)3(eta-C5H5)] afforded the edge-bridged tetrahedral cluster [W2Ir3(mu4-eta2-C2Ph)(mu-CO)(CO)9(eta-C5H5)(eta-C5Me5)] (3) and the edge-bridged trigonal-bipyramidal cluster [W3Ir3(mu4-eta2-C2Ph)(mu-eta2-C=CHPh)(Cl)(CO)8(eta-C5Me5)(eta-C5H5)2] (4) in poor to fair yield. Cluster 3 forms by insertion of [W(C[triple bond]CPh)(CO)3(eta-C5H5)] into Ir-Ir and W-Ir bonds, accompanied by a change in coordination mode from a terminally bonded alkynyl to a mu4-eta2 alkynyl ligand. Cluster 4 contains an alkynyl ligand interacting with two iridium atoms and two tungsten atoms in a mu4-eta2 fashion, as well as a vinylidene ligand bridging a W-W bond. Reaction of [WIr3(CO)11(eta-C5H5)] (1a) or 1c with [(eta-C5H5)(CO)2 Ru(C[triple bond]C)Ru(CO)2(eta-C5H5)] afforded [Ru2WIr3(mu5-eta2-C2)(mu-CO)3(CO)7(eta-C5H5)2(eta-C5R5)] [R = H (5a), Me (5c)] in low yield, a structural study of 5a revealing a WIr3 butterfly core capped and spiked by Ru atoms; the diruthenium ethyndiyl precursor has undergone Ru-C scission, with insertion of the C2 unit into a W-Ir bond of the cluster precursor. Reaction of [W2Ir2(CO)10(eta-C5H5)2] with the diruthenium ethyndiyl reagent gave [RuW2Ir2{mu4-eta2-(C2C[triple bond]C)Ru(CO)2(eta-C5H5)}(mu-CO)2(CO)6(eta-C5H5)3] (6) in low yield, a structural study of 6 revealing a butterfly W2Ir2 unit capped by a Ru(eta-C5H5) group resulting from Ru-C scission; the terminal C2 of a new ruthenium-bound butadiyndiyl ligand has been inserted into the W-Ir bond. Reaction between 1a, [WIr3(CO)11(eta-C5H4Me)] (1b), or 1c and [(eta-C5H5)(CO)3W(C[triple bond]CC[triple bond]C)W(CO)3(eta-C5H5)] afforded [W2Ir3{mu4-eta2-(C2C[triple bond]C)W(CO)3(eta-C5H5)}(mu-CO)2(CO)2(eta-C5H5)(eta-C5R5)] [R = H (7a), Me (7c); R5 = H4Me (7b)] in good yield, a structural study of 7c revealing it to be a metallaethynyl analogue of 3.     

Synthesis of Tungsten Carbonyl and Nitrosyl Complexes of Monodentate and Chelating Aryl-N-sulfonylphosphoramides, the First Members of a New Class of Electron-Withdrawing Phosphine Ligands. Comparative IR and (13)C and (31)P NMR Study of Related Phosphorus Complexes

Reaction of N,N'-bis(tolylsulfonyl)-1,2-diaminoethane with PhPCl(2) gives in 62% yield the phosphonous diamide 2-phenyl-1,3-bis(p-tolylsulfonyl)-1,3,2-diazaphospholidine (4, "TosL") and with Ph(2)PCl in 43% yield the diphosphinous amide N,N'-bis(diphenylphosphino)-N,N'-bis(p-tolylsulfonyl)-1,2-ethanediamine (5, "diTosL"). Reaction of 4 with (THF)W(CO)(5) gives (TosL)W(CO)(5) (6) in 77% yield, and reaction of 5 with trans-BrW(CO)(4)NO gives cis, cis, trans-(diTosL)W(CO)(2)(NO)Br (8) in 86% yield. The IR, (13)C NMR, and (31)P NMR spectra of 4, 5, 6, and 8 are compared to those of a variety of compounds including LW(CO)(5) (L = PMe(3), PPh(3), PPh(NEt(2))(2), P(OMe)(3), P(CF(3))(3)), L(2)W(CO)(2)(NO)Br (L(2) = Ar(2)PCH(2)CH(2)PAr(2) (Ar = Ph (diphos), C(6)F(5) (diphos-F(20))), (CH(3)CN)(2)), and the free ligands as appropriate. The IR data are interpreted to suggest a relative ordering of ligand acceptor ability of P(CF(3))(3) > 4 approximately P(OMe)(3) > PPh(3) approximately PPh(NEt(2))(2) and a relative ordering of ligand donor ability of PPh(NEt(2))(2) >/= P(OMe)(3) > PPh(3) > 4 > P(CF(3))(3). The chelating ligand diTosL is about as electron-withdrawing as diphos-F(20), on the basis of the IR data. The (31)P NMR data qualitatively support the conclusion that TosL and diTosL are highly electron-withdrawing ligands, on the basis of (1)J(PW). The (13)C data do not permit any such generalizations, although the spectra of the diphosphine ligands and adducts are of interest due to the observation of "virtual coupling" that surprisingly can be simulated only as ABX rather than AA'X spin-systems.     

Low-temperature N-O bond cleavage of nitrogen monoxide in heterometallic carbonyl complexes. An experimental and theoretical study

The reaction of Na[RuCp(CO) 2] with [MnCp'(CO) 2(NO)]BF 4 gives the corresponding heterometallic derivative [MnRuCpCp'(mu-CO) 2(CO)(NO)] (Cp = eta (5)-C 5H 5; Cp' = eta (5)-C 5H 4Me). In contrast, the group 6 metal carbonyl anions [MCp(CO) 2L] (-) (M = Mo, W; L = CO, P(OMe) 3, PPh 3) react with the Mn and Re complexes [M'Cp'(CO) 2(NO)]BF 4 to give the heterometallic derivatives [MM'CpCp'(mu-N)(CO) 3L] having a nitride ligand linearly bridging the metal centers (W-N = 1.81(3) A, N-Re = 1.97(3) A, W-N-Re = 179(1) (o), in [WReCpCp'(mu-N)(CO) 3{P(OMe) 3}]). Density-functional theory calculations on the reactions of [WCp(CO) 3] (-) and [RuCp(CO) 2] (-) with [MnCp(CO) 2(NO)] (+) revealed a comparable qualitative behavior. Thus, two similar and thermodynamically allowed reaction pathways were found in each case, one implying the displacement of CO from the cation and formation of a metal-metal bond, the other implying the cleavage of the N-O bond of the nitrosyl ligand and release of a carbonyl from the anion as CO 2. The second pathway is more exoergonic and is initiated through an orbitally controlled attack of the anion on the N atom of the NO ligand in the cation. In contrast, the first pathway is initiated through a charge-controlled attack of the anion to the C atom of a CO ligand in the cation. The CO 2-elimination pathway requires at the intermediate stages a close approach of the NO and CO ligands, which is more difficult for the Ru compound because of its lower coordination number (compared to W). This effect, when combined with a stronger stabilization of the initial intermediate in the Ru reaction, makes the CO 2-elimination pathway slower in that case.     

Carbonyl complexes of platinum(0): synthesis and structure of [(Cy3P)2Pt(CO)] and [(Cy3P)2Pt(CO)2

The platinum(0) monocarbonyl complex, [(Cy(3)P)(2)Pt(CO)], was synthesized by reaction of [(Cy(3)P)(2)Pt] with [(η(5)-C(5)Me(5))Ir(CO)(2)] and subsequent irradiation. X-ray structure analysis was performed and represents the first structural evidence of a platinum(0) monocarbonyl complex bearing two free phosphine ligands. Its corresponding dicarbonyl complex [(Cy(3)P)(2)Pt(CO)(2)] was synthesized by treatment of [(Cy(3)P)(2)Pt] with CO at -40 °C and confirmed by X-ray structure analysis.     

Reactions of the transient species Cr(CO)5(cyclohexane) with C4HnE (n=4, 8; E=O, NH, S) studied by time-resolved IR absorption spectroscopy

Time-resolved IR absorption spectroscopy is used to investigate substitution of the cyclohexane (CyH) molecule of the photolytically generated alkane-solvated transient intermediate Cr(CO)5(CyH) by heterocyclic ligands C4HnE (n=4, 8; E=O, NH, S). From the concentration and temperature dependences of the pseudo-first order rate constants, we obtain activation parameters for the reactions, and find that they are consistent with an associative (A) or interchange (I) mechanism. As was the case with ligand substitution reactions at W(CO)5(CyH), a ligand's reactivity depends both on its electron-donating ability and on its polarizability. We also find that for a reaction with a given DeltaH, the activation entropy is higher for reaction of Cr(CO)5(CyH) than it is for reaction of W(CO)5(CyH). Comparison of the present results with ligand substitution reactions of W(CO)5(CyH), CpMn(CO)2(CyH), and Cr(CO)5(n-heptane) indicates that for ligand substitution reactions at alkane-solvated transition-metal intermediates, the solvent's effect upon the reaction rate is primarily entropic.     

Complexes with a Metal-Phosphorus Triple Bond as Versatile Building Blocks in Coordination and Organometallic Chemistry

Trapping reactions of the phosphido complex intermediate [Cp*(CO) 2 W L P M W(CO) 5 ], generated by thermolysis of [Cp*P{W(CO) 5 } 2 ] 1 , occur via [2 + 2] cycloaddition reactions with P 4 , phosphaalkynes, alkynes, and [CpMo(CO) 2 ] 2 , respectively. However, with nitriles, insertion reactions into the P--C bond of 1 are observed already at room temperature to give novel P-containing heterocycles. Furthermore, irradiation of 1 gives the tetrahedral complex [Cp*(CO) 6 W 2 }( w -H)( w , m 2 -P 2 ){W(CO) 5 } 2 ], which indicates that besides the formation of the triple-bond intermediate [Cp*(CO) 2 W L P M W(CO) 5 ] a second Cp* elimination intermediate of the type [P{W(CO) 5 } 2 ] occurs.     

Reactions of the tertiary phosphines R2PCCCl(CF2)n with group VI hexacarbonyls and salts of platinum and palladium

The tertiary phosphines R₂P$\text{CCCl(C}$F₂)_n (R = C₆H₅ or C₆H₁₁; n = 2,3, or 4) react with M(CO)₆ (M = Cr, Mo, W) to give R₂P$\text{CCCl(C}$F₂)_nM(CO)₅ in which the ligand is bonded to M through P alone. Similar bonding is found in some chloro-complexes of platinum and palladium.     

Reaction of [M(eta3-allyl)(eta2-amidinato)(CO)2(pyridine)] complexes (M = Mo, W) with bidentate ligands: nitrogen donor vs. phosphorus donor

The reactivity of amidinato complexes of molybdenum and tungsten bearing pyridine as a labile ligand, [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)(pyridine)](M = Mo; 1-Mo, M = W; 1-W), toward bidentate ligands such as 1,10-phenanthroline (phen) and 1,2-bis(diphenylphosphino)ethane (dppe) was investigated. The reaction of 1 with phen at ambient temperature resulted in the formation of monodentate amidinato complexes, [M(eta(3)-allyl)(eta(1)-amidinato)(CO)(2)(eta(2)-phen)](M = Mo; 2-Mo, M = W; 2-W), which has pseudo-octahedral geometry with the amidinato ligand coordinated to the metal in an eta(1)-fashion. The phen ligand was located coplanar with two CO ligands and the eta(1)-amidinato ligand was positioned trans to the eta(3)-allyl ligand. In solution, both complexes 2-Mo and 2-W showed fluxionality, and complex 2-Mo afforded allylamidine (3) on heating in solution. In the reaction of 1 with dppe at ambient temperature, the simple substitution reaction took place to give dppe-bridged binuclear complexes [{M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)}(2)(mu-dppe)](M = Mo; 5-Mo, M = W; 5-W), whereas mononuclear monocarbonyl complexes [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(eta(2)-dppe)](M = Mo; 6-Mo, M = W; 6-W) were obtained under acetonitrile- or toluene-refluxing conditions. Mononuclear complex 6 was also obtained by the reaction of binuclear complex 5 with 0.5 equivalents of dppe under refluxing in acetonitrile or in toluene. The X-ray analyses and variable-temperature (31)P NMR spectroscopy of complex 6 indicated the existence of the rotational isomers of the eta(3)-allyl ligand, i.e., endo and exo forms, with respect to the carbonyl ligand. The different reactivity of complex 1 toward phen and dppe seems to have come from the difference in the pi-acceptability of each bidentate ligand.     

Transition‐Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group 14 Atoms (E=C–Sn) as Ligands; Part 2: Complexation with W(CO)5

Density functional calculations at the BP86/TZ2P level were carried out to understand the ligand properties of the 16‐valence‐electron(VE) Group 14 complexes [(PMe₃)₂Cl₂M(E)] ( 1ME ) and the 18‐VE Group 14 complexes [(PMe₃)₂(CO)₂M(E)] ( 2ME ; M=Fe, Ru, Os; E=C, Si, Ge, Sn) in complexation with W(CO)₅. Calculations were also carried out for the complexes (CO)₅W–EO. The complexes [(PMe₃)₂Cl₂M(E)] and [(PMe₃)₂(CO)₂M(E)] bind strongly to W(CO)₅ yielding the adducts 1ME–W(CO)₅ and 2ME–W(CO)₅ , which have C_2v equilibrium geometries. The bond strengths of the heavier Group 14 ligands 1ME (E=Si–Sn) are uniformly larger, by about 6–7 kcal mol^?1, than those of the respective EO ligand in (CO)₅W‐EO, while the carbon complexes 1MC–W(CO)₅ have comparable bond dissociation energies (BDE) to CO. The heavier 18‐VE ligands 2ME (E=Si–Sn) are about 23–25 kcal mol^?1 more strongly bonded than the associated EO ligand, while the BDE of 2MC is about 17–21 kcal mol^?1 larger than that of CO. Analysis of the bonding with an energy‐decomposition scheme reveals that 1ME is isolobal with EO and that the nature of the bonding in 1ME–W(CO)₅ is very similar to that in (CO)₅W–EO. The ligands 1ME are slightly weaker π acceptors than EO while the π‐acceptor strength of 2ME is even lower.     

Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3‐Dipnictabutadienes

The reaction of the phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 a ) with diphenyldiazomethane leads to [{W(CO)₅}Cp*P=NN{W(CO)₅}=CPh₂] ( 2 ). Compound 2 is a rare example of a phosphadiazadiene ligand (R‐P=N?N=CR′R′′) complex. At temperatures above 0 °C, 2 decomposes into the complex [{W(CO)₅}PCp*{N(H)N=CPh₂)₂] ( 3 ), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO)₅}₂] (E=P, As) with diazomethane (CH₂NN) proceeds differently. For the arsinidene complex ( 1 b ), only the arsaalkene complex 4 b [{W(CO)₅}₂{η^1:2‐(Cp*)As=CH₂}] is formed. The reaction with the phosphinidene complex ( 1 a ) results in three products, the two phosphaalkene complexes [{W(CO)₅}₂{η^1:2‐(R)P=CH₂}] ( 4 a : R=Cp*, 5 : R=H) and the triazaphosphole derivative [{W(CO)₅}P(Cp*)‐CH₂‐N{W(CO)₅}=N‐N(N=CH₂)] ( 6 a ). The phosphaalkene complex ( 4 a ) and the arsaalkene complex ( 4 b ) are not stable at room temperature and decompose to the complexes [{W(CO)₅}₄(CH₂=E?E=CH₂)] ( 7 a : E=P, 7 b : E=As), which are the first examples of complexes with parent 2,3‐diphospha‐1,3‐butadiene and 2,3‐diarsa‐1,3‐butadiene ligands.     

New diphosphine ligands containing ethyleneglycol and amino alcohol spacers for the rhodium-catalyzed carbonylation of methanol

The new diphosphine ligands Ph(2)PC(6)H(4)C(O)X(CH(2))(2)OC(O)C(6)H(4)PPh(2) (1: X=NH; 2: X=NPh; 3: X=O) and Ph(2)PC(6)H(4)C(O)O(CH(2))(2)O(CH(2))(2)OC(O)C(6)H(4)PPh(2) (5) as well as the monophosphine ligand Ph(2)PC(6)H(4)C(O)X(CH(2))(2)OH (4) have been prepared from 2-diphenylphosphinobenzoic acid and the corresponding amino alcohols or diols. Coordination of the diphosphine ligands to rhodium, iridium, and platinum resulted in the formation of the square-planar complexes [(Pbond;P)Rh(CO)Cl] (6: Pbond;P=1; 7: Pbond;P=2; 8: Pbond;P=3), [(Pbond;P)Rh(CO)Cl](2) (9: Pbond;P=5), [(P-P)Ir(cod)Cl] (10: Pbond;P=1; 11: Pbond;P=2; 12: Pbond;P=3), [(Pbond;P)Ir(CO)Cl] (13: Pbond;P=1; 14: Pbond;P=2; 15: Pbond;P=3), and [(Pbond;P)PtI(2)] (18: Pbond;P=2). In all complexes, the diphosphine ligands are trans coordinated to the metal center, thanks to the large spacer groups, which allow the two phosphorus atoms to occupy opposite positions in the square-planar coordination geometry. The trans coordination is demonstrated unambiguously by the single-crystal X-ray structure analysis of complex 18. In the case of the diphosphine ligand 5, the spacer group is so large that dinuclear complexes with ligand 5 in bridging positions are formed, maintaining the trans coordination of the P atoms on each metal center, as shown by the crystal structure analysis of 9. The monophosphine ligand 4 reacts with [[Ir(cod)Cl](2)] (cod=cyclooctadiene) to give the simple derivative [(4)Ir(cod)Cl] (16) which is converted into the carbonyl complex [(4)Ir(CO)(2)Cl] (17) with carbon monoxide. The crystal structure analysis of 16 also reveals a square-planar coordination geometry in which the phosphine ligand occupies a position cis with respect to the chloro ligand. The diphosphine ligands 1, 2, 3, and 5 have been tested as cocatalysts in combination with the catalyst precursors [[Rh(CO)(2)Cl](2)] and [[Ir(cod)Cl](2)] or [H(2)IrCl(6)] for the carbonylation of methanol at 170 degrees C and 22 bar CO. The best results (TON 800 after 15 min) are obtained for the combination 2/[[Rh(CO)(2)Cl](2)]. After the catalytic reaction, complex 7 is identified in the reaction mixture and can be isolated; it is active for further runs without loss of catalytic activity.     

Synthesis of benzannulated N-heterocyclic carbene ligands by a template synthesis from 2-nitrophenyl isocyanide

The reaction of 2-nitrophenyl isocyanide 2 with [M(CO)5(thf)] (M=Cr, Mo, W) yields the isocyanide complexes [M(CO)5(2)] (3: M=Cr; 4: M=Mo; 5: M=W). Complexes 3-5 react with elemental tin under reduction of the nitro function of the isocyanide ligand to give the complexes with the unstable 2-aminophenyl isocyanide ligand. The coordinated 2-aminophenyl isocyanide ligand in all three complexes reacts spontaneously under intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the complexes with the NH,NH-benzimidazol-2-ylidene ligand (6: M=Cr; 7: M=Mo; 8: M=W). An incomplete reduction of the nitro group in 3-5 is observed when hydrazine hydrate is used instead of tin. Here the formation of complexes with a coordinated 2-hydroxylamine-functionalized phenyl isocyanide [(CO)5M-CN-C6H(4-)-2-N(H)-OH] is postulated and this unstable ligand again undergoes intramolecular cyclization to give the NH,NOH-stabilized benzimidazol-2-ylidene complexes 9-11. The tungsten derivative 11 can be allylated stepwise by a deprotonation/alkylation sequence first at the OH and then at the NH position to yield the monoallylated and diallylated species 12 and 13. The molecular structures of 3-5 and 12-13 were established by X-ray crystallography.     

EPR and DFT studies of the structure of phosphinyl radicals complexed by a pentacarbonyl transition metal

Paramagnetic complexes M(CO)5P(C6H5)2, with M = Cr, Mo, W, have been trapped in irradiated crystals of M(CO)5P(C6H5)3 (M = Cr, Mo, W) and M(CO)5PH(C6H5)2 (M = Cr, W) and studied by EPR. The radiolytic scission of a P-C or a P-H bond, responsible for the formation of M(CO)5P(C6H5)2, is consistent with both the number of EPR sites and the crystal structures. The g and 31P hyperfine tensors measured for M(CO)5P(C6H5)2 present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph2P*, the 31P isotropic coupling is larger, the dipolar coupling is smaller, and for Mo and W compounds, the g-anisotropy is more pronounced. These properties are well predicted by DFT calculations. In the optimized structures of M(CO)5P(C6H5)2 (M = Cr, Mo, W), the unpaired electron is mainly confined in a phosphorus p-orbital, which conjugates with the metal d(xz) orbital. The trapped species can be described as a transition metal-coordinated phosphinyl radical.     

Reactivity of transition metal-phosphorus triple bonds towards triply bonded [{CpMo(CO)2}2]: formation of heteronuclear cluster compounds

Thermolysis of [Cp*P{W(CO)5}2] (1) in the presence of [{CpMo(CO)2}2] leads to the novel complexes [{(CO)2Cp*W}{CpMo(CO)2}(micro,eta2:eta1:eta1-P2{W(CO)5}2)] (6; Cp=eta5-C5H5, Cp*=eta5-C5Me5), [{(micro-O)(CpMoWCp*)W(CO)4}{micro3-PW(CO)5}2] (7), [{CpMo(CO)2}2{Cp*W(CO)2}{micro3-PW(CO)5}] (8) and [{CpMo(CO)2}2{Cp*W(CO)2}(micro3-P)] (9). The structural framework of the main products 8 and 9 can be described as a tetrahedral Mo2WP unit that is formed by a cyclisation reaction of [{CpMo(CO)2}2] with an [Cp*(CO)2W[triple chemical bond]P-->W(CO)5] intermediate containing a W--P triple bond and subsequent metal-metal and metal-phosphorus bond formation. Photolysis of 1 in the presence of [{CpMo(CO)2}2] gives 8, 9 and phosphinidene complex [(micro3-PW(CO)5){CpMo(CO)2W(CO)5}] (10), in which the P atom is in a nearly trigonal-planar coordination environment formed by one {CpMo(CO)2} and two {W(CO)5} units. Comprehensive structural and spectroscopic data are given for the products. The reaction pathways are discussed for both activation procedures, and DFT calculations reveal the structures with minimum energy along the stepwise Cp* migration process under formation of the intermediate [Cp*(CO)2W[triple chemical bond]P-->W(CO)5].     

An experimental and theoretical investigation of the carbon dioxide insertion process into the tungsten-nitrogen bond of an anionic W(0) complex

The pyridine bound 2-aminopyridine (2APH) derivative of tungsten pentacarbonyl has been prepared from photogenerated W(CO)5THF and 2APH. Deprotonation of the distal amine group by sodium hydride has provided two complexes, [Na][W(CO)5(2AP)] and [Na]2[W(CO)4(2AP)]2. Both complexes have been characterized by X-ray crystallography with the monomeric derivative being crystallized as its [Na2(18-crown-6)][W(CO)5(2AP)]2 salt which exhibits strong Na+...-NH interactions. Photolysis of W(CO)6 in the presence of excess 2-aminopyridine in THF has led to an efficient synthesis of the chelated neutral derivative, W(CO)4(2APH).2APH, where the extra equivalent of 2APH is hydrogen bonded to its bound counterpart. The 2-aminopyridine molecule of solvation was almost quantitatively removed via aqueous washings. Deprotonation of W(CO)4(2APH) with NaH afforded the amidopyridine derivative which was shown to rapidly undergo reaction with CO2 to yield the chelated carbamate complex, W(CO)4(OC(O)2AP)-. Nevertheless, because of the presence of small quantities of free 2-aminopyridine during the reactions with CO2, we have not been able to conclusively rule out participation by a ligand substitution process involving NC5H4NHCOOH. Ab initio computations were found to substantiate many of these experimental observations. That is, in the monodentate bound W(CO)5(2APH) derivative, binding through the pyridine nitrogen atom is favored by about 29 kJ/mol over the amine nitrogen atom, whereas the opposite site for binding is preferred for the deprotonated amido analogue, W(CO)5(2AP)-. Furthermore, both forms of W(CO)5(2AP)- were found to be more stable than the chelated tungsten tetracarbonyl anion plus CO. On the other hand, CO2 insertion into the W(CO)4(2AP)- anion to provide the chelated carbamate, W(CO)4(OC(O)2AP)-, was thermodynamically favored by >110 kJ/mol. Finally, both experimental and theoretical studies were inconclusive with regard to identifying reaction intermediates during the CO2 insertion pathway which involve prior interactions of CO2 at the amido nitrogen center.     

Stepwise Formation of a 1,3‐Butadiene Analogue of Mixed Heavier Group 15 Elements

The reaction of the phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 a ) with di‐tert‐butylcarboimidophosphene leads to the P? C cage compound 6 and the Lewis acid–base adduct [Cp*P{W(CO)₅}₂(CNtBu)] ( 2 a ). In contrast, the arsinidene complex shows a different reactivity. At low temperatures, the arsaphosphene complex [{W(CO)₅}{η²‐(Cp*)As?P(tBu)}{W(CO)₅}] ( 3 ) is formed. At these temperatures, 3 reacts further with a second equivalent of carboimidophosphene to form [{W(CO)₅}{η²‐{(Cp*)(tBu)P}As?P(tBu)}{W(CO)₅}] ( 5 ), probably by the insertion of a phosphinidene unit (tBuP) into an As? C bond. In contrast, at room temperature 3 reacts further by a radical‐type reaction to form [{(tBu)P?As? As?P(tBu)}{W(CO)₅}₄] ( 4 ). Compound 4 is the first example of a neutral, 1,3‐butadiene analogue containing only mixed heavier Group 15 elements. It consists of two P?As double bonds connected by arsenic atoms.