H2 activation in aqueous solution: formation of trans-[Fe(DMeOPrPE)2H(H2)]+ via the heterolysis of H2 in water

The water-soluble iron phosphine complex trans-Fe(DMeOPrPE)(2)Cl(2) (DMeOPrPE = 1,2-bis(bis(methoxypropyl)phosphino)ethane) reacts with H(2) in water to produce trans-[Fe(DMeOPrPE)(2)H(H(2))](+) and H(+). The product is a water-soluble eta(2)-H(2) metal hydride complex, formed via the heterolysis of coordinated H(2) in water.     

Coordination of a complete series of N2 reduction intermediates (N2H2, N2H4, and NH3) to an iron phosphine scaffold

The series of dinitrogen reduction intermediates (N(2)H(2), N(2)H(4), and NH(3)) coordinated to the Fe(DMeOPrPE)(2)H(+)(DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane) scaffold has been synthesized or generated. The synthesis of trans-[Fe(DMeOPrPE)(2)(NH(3))H][BPh(4)] and generation of trans-[Fe(DMeOPrPE)(2)(N(2)H(4))H][BPh(4)] were achieved by substitu tion of the dinitrogen ligand on trans-[Fe(DMeOPrPE)(2)(N(2))H][BPh(4)]. The trans-[Fe(DMeOPrPE)(2)(N(2)H(2))H](+) complex and its deprotonated conjugate base, trans-Fe(DMeOPrPE)(2)(N(2)H)H, were observed by (31)P and (1)H NMR from decomposition of trans-[Fe(DMeOPrPE)(2)(N(2)H(4))H](+) in the presence of excess hydrazine. Attempts to chemically oxidize trans-[Fe(DMeOPrPE)(2)(N(2)H(4))H](+) to trans-[Fe(DMeOPrPE)(2)(N(2)H(2))H][BPh(4)] with a variety of oxidizing agents yielded only decomposition products consistent with the intermediate formation of trans-[Fe(DMeOPrPE)(2)(N(2)H(2))H](+) prior to decomposition.     

Coordination chemistry of H2 and N2 in aqueous solution. Reactivity and mechanistic studies using trans-FeII(P2)2X2)-type complexes (P2 = a chelating, water-solubilizing phosphine)

The reactions of the trans-Fe(DMeOPrPE)2Cl2 complex (I; DMeOPrPE = 1,2-bis(bis(methoxypropyl)phosphino)ethane) and its derivatives were studied in aqueous and nonaqueous solvents with a particular emphasis on the binding and activation of H2 and N2. The results show there are distinct differences in the reaction pathways between aqueous and nonaqueous solvents. In water, I immediately reacts to form trans-Fe(DMeOPrPE)2(H2O)Cl+. Subsequent reaction with H2 or N2 yields trans-Fe(DMeOPrPE)2(X2)Cl+ (X2=H2 or N2). In the case of H2, further reactivity occurs to ultimately give the trans-Fe(DMeOPrPE)2(H2)H+ product (III). The pathway for the reaction I --> III was spectroscopically examined: following the initial loss of chloride and replacement with H2, heterolysis of the H2 ligand occurs to form Fe(DMeOPrPE)2(H)Cl; substitution of the remaining chloride ligand by another H2 molecule then occurs to produce trans-Fe(DMeOPrPE)2(H2)H+. In the absence of H2 or N2, trans-Fe(DMeOPrPE)2(H2O)Cl+ slowly reacts in water to form Fe(DMeOPrPE)32+, II. Experiments showed that this species forms by reaction of free DMeOPrPE ligand with trans-Fe(DMeOPrPE)2(H2O)Cl+, where the free DMeOPrPE ligand comes from dissociation from the trans-Fe(DMeOPrPE)2(H2O)Cl+ complex. In nonaqueous solvents, the chloride ligand in I is not labile, and a reaction with H2 only occurs if a chloride abstracting reagent is present. Complex III is a useful synthon for the formation of other water-soluble metal hydrides. For example, the trans-[Fe(DMeOPrPE)2H(N2)]+ complex was generated in H2O by substitution of N2 for the H2 ligand in III. The trans-Fe(DHBuPE)2HCl complex (DHBuPE = 1,2-bis(bis(hydroxybutyl)phosphino)ethane, another water-solubilizing phosphine) was shown to be a viable absorbent for the separation of N2 from CH4 in a pressure swing scheme. X-ray crystallographic analysis of II is the first crystal structure report of a homoleptic tris chelate of FeII containing bidentate phosphine ligands. The structure reveals severe steric crowding at the Fe center.     

Ring-opening reaction of phosphorus-bridged [1]ferrocenophane via ring slippage from eta(5)- to eta(1)-Cp

A reaction mechanism was investigated for a ring-opening reaction of RP(E)-bridged [1]ferrocenophane, where RP(E) = PhP(S) (3a), PhP (3b), and MesP (3c) (Mes = 2,4,6-trimethylphenyl). Irradiation of UV-vis light in the presence of an excess amount of P(OMe)(3) transformed 3a to [Fe(PhP(S)(eta(5)-C(5)H(4))(eta(1)-C(5)H(4)))(P(OMe)(3))(2)] (4a), in which one of the two cyclopentadienyl (Cp) rings of 3a changed its coordination mode from eta(5) to eta(1) and vacant coordination sites thus formed on the iron center were occupied by two P(OMe)(3) ligands. The molecular structure of 4a was determined by X-ray analysis, in which eta(1)-Cp adopted a 1-Fe-2-P-1,3-cyclopentadiene structure. Under the same reaction conditions, 3b and 3c also gave similar ring-slipped products 4b and 4c, respectively. Photolysis of 3a using more strongly coordinating PMe(3) in place of P(OMe)(3) led to complete dissociation of a Cp ligand from the iron center to form [Fe(PhP(S)(eta(5)-C(5)H(4))(C(5)H(4)))(PMe(3))(3)] (5). The formation of the ring-slipped and -dissociated products on the photolysis of 3 strongly supports the view that photolytic ring-opening polymerization of 3 proceeds via an unprecedented Fe-Cp bond cleavage mechanism.     

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.     

Solution structures and dynamic properties of chelated d(0) metal olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) (R = H, Me): Models for the [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" catalysts.

To model the Ti-olefin interaction in the putative [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" Ti-catalyzed olefin polymerization, chelated alkoxide olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) have been investigated. The reaction of [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(2) (1a,b; R = H, Me) with HOCMe(2)CH(2)CH(2)CH=CH(2) yields mixtures of [eta(5)-C(5)R(4)SiMe(2)NH(t)Bu]TiMe(2)(OCMe(2)CH(2)CH(2)CH=CH(2)) (2a,b) and [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(OCMe(2)CH(2)CH(2)CH=CH(2)) (3a,b). The reaction of 2a/3a and 2b/3b mixtures with B(C(6)F(5))(3) yields the chelated olefin complexes [[eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][MeB(C(6)F(5))(3)] (4a,b; 71 and 89% NMR yield). The reaction of 2b/3b with [Ph(3)C][B(C(6)F(5))(4)] yields [[eta(5): eta(1)-C(5)Me(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][B(C(6)F(5))(4)] (5b, 88% NMR yield). NMR studies establish that 4a,b and 5b exist as mixtures of diastereomers (isomer ratios: 4a/4a', 62/38; 4b/4b', 75/25; 5b/5b', 75/25), which differ in the enantioface of the olefin that is coordinated. NMR data for these d(0) metal olefin complexes show that the olefin coordinates to Ti in an unsymmetrical fashion primarily through C(term) such that the C=C pi bond is polarized with positive charge buildup on C(int). Dynamic NMR studies show that 4b/4b' undergoes olefin face exchange by a dissociative mechanism which is accompanied by fast inversion of configuration at Ti ("O-shift") in the olefin-dissociated intermediate. The activation parameters for the conversion of 4b to 4b' (i.e., 4b/4b' face exchange) are: DeltaH = 17.2(8) kcal/mol; DeltaS = 8(1) eu. 4a/4a' also undergoes olefin face exchange but with a lower barrier (DeltaH = 12.2(9) kcal/mol; DeltaS = -2(3) eu), for the conversion of 4a to 4a'.     

Photochemical reactions of [CH2(eta5-C5H4)2][Rh(C2H4)2]2 with silanes: evidence for Si-C and C-H activation pathways

Photochemical reaction of [CH2(eta5-C5H4)2][Rh(C2H4)2]2 1 with dmso led to the stepwise formation of [CH2(eta5-C5H4)2][Rh(C2H4)2][Rh(C2H4)(dmso)] 2a and [CH2(eta5-C5H4)2][Rh(C2H4)(dmso)]2 2b. Photolysis of 1 with vinyltrimethylsilane ultimately yields three isomeric products of [CH2(eta5-C5H4)2][Rh(CH2=CHSiMe3)2]2, 3a, 3b and 3c which are differentiated by the relative orientations of the vinylsilane. When this reaction is undertaken in d6-benzene, H/D exchange between the solvent and the alpha-proton of the vinylsilane is revealed. In addition evidence for two isomers of the solvent complex [CH2(eta5-C5H4)2][Rh(C2H4)2][Rh(C2H4)(eta2-toluene)] was obtained in these and related experiments when the photolysis was completed at low temperature without substrate, although no evidence for H/D exchange was observed. Photolysis of 1 with Et3SiH yielded the sequential substitution products [CH2(eta5-C5H4)2][Rh(C2H4)2][Rh(C2H4)(SiEt3)H] 4a, [CH2(eta5-C5H4)2][Rh(C2H4)(SiEt3)H]2 4b, [CH2(eta5-C5H4)2][Rh(C2H4)(SiEt3)H][Rh(SiEt3)2(H)2] 4c and [CH2(eta5-C5H4)2][Rh(SiEt3)2(H)2]2 4d; deuteration of the alpha-ring proton sites, and all the silyl protons, of 4d was demonstrated in d6-benzene. This reaction is further complicated by the formation of two Si-C bond activation products, [CH2(eta5-C5H4)2][RhH(mu-SiEt2)]2 5 and [CH2(eta5-C5H4)2][(RhEt)(RhH)(mu-SiEt2)2] 6. Complex 5 was also produced when 1 was photolysed with Et2SiH2. When the photochemical reactions with Et3SiH were repeated at low temperatures, two isomers of the unstable C-H activation products, the vinyl hydrides [CH2(eta5-C5H4)2][{Rh(SiEt3)H}{Rh(SiEt3)}(mu-eta1,eta2-CH=CH2)] 7a and 7b, were obtained. Thermally, 4c was shown to form the ring substituted silyl migration products [(eta5-C5H4)CH2(C5H3SiEt3)][Rh(SiEt3)2(H)2]2 8 while 4b formed [CH2(C5H3SiEt3)2][Rh(SiEt3)2(H)2]2 (9a and 9b) upon reaction with excess silane. The corresponding photochemical reaction with Me3SiH yielded the expected products [CH2(eta5-C5H4)2][Rh(C2H4)2][Rh(C2H4)(SiMe3)H] 10a, [CH2(eta5-C5H4)2][Rh(C2H4)(SiMe3)H]2 10b, [CH2(eta5-C5H4)2][Rh(C2H4)(SiMe3)H][Rh(SiMe3)2(H)2] 10c and [CH2(eta5-C5H4)2][Rh(SiMe3)2(H)2]2 10d. However, three Si-C bond activation products, [CH2(eta5-C5H4)2][(RhMe)(RhH)(mu-SiMe2)2] 11, [CH2(eta5-C5H4)2][(Rh{SiMe3})(RhMe)(mu-SiMe2)2] 12 and [CH2(eta5-C5H4)2][(Rh{SiMe3})(RhH)(mu-SiMe2)2] 13 were also obtained in these reactions.     

Heterobimetallic, cubane-like Mo(3)S(4)M' cluster cores containing the noble metals M' = Ru, Os, Rh, Ir. Unprecedented tri(mu-carbonyl) bridge between ruthenium atoms in [(eta(5)-Cp')(3)Mo(3)S(4)Ru)2(mu-CO)3]2+

Reaction of the methylcyclopentadienyl (Cp') cluster compound [(eta(5)-Cp')(3)Mo(3)S(4)][pts] (pts = p-toluenesulfonate) with noble metal alkene complexes resulted in the formation of four new heterobimetallic cubane-like Mo(3)S(4)M' cluster cores (M' = Ru, Os, Rh, Ir). Thus, reaction with [(1,5-cod)Ru(CO)(3)] or [(1,3-cod)Os(CO)(3)] (cod = cyclooctadiene) afforded [(eta(5)-Cp')(3)Mo(3)S(4)M'(CO)(2)][pts] (M' = Ru: [1][pts]; M' = Os: [2][pts]). When [1][pts] was kept in CH(2)Cl(2)/pentane solution, partial loss of carbonyl ligands occurred and the carbonyl-bridged dicubane cluster [((eta(5)-Cp')(3)Mo(3)S(4)Ru)(2)(mu-CO)(3)][pts](2) was isolated. An X-ray crystal structure revealed the presence of the hitherto unobserved Ru(mu-CO)(3)Ru structural element. The formation of cluster compounds containing Mo(3)S(4)Rh and Mo(3)S(4)Ir cores was achieved in boiling methanol by reacting [(eta(5)-Cp')(3)Mo(3)S(4)][pts] with [M'Cl(cyclooctene)(2)](2) (M' = Rh, Ir) in the presence of PPh(3). In this way [(eta(5)-Cp')(3)Mo(3)S(4)M'Cl(PPh(3))][pts] (M' = Rh, Ir) could be isolated. An alternative route to the Mo(3)S(4)Rh cluster core was found in the reaction of [(eta(5)-Cp')(3)Mo(3)S(4)][pts] with [RhCl(1,5-cod)](2), which yielded [(eta(5)-Cp')(3)Mo(3)S(4)Rh(cod)][pts](2) ([7][pts](2)). Substitution of the cod ligand in [7][pts](2) by 1,3-bis(diphenylphosphanyl)propane (dppp) gave [(eta(5)-Cp')(3)Mo(3)S(4)Rh(dppp)][pts](2).     

Coordinatively unsaturated semisandwich complexes of ruthenium with phosphinoamine ligands and related species: a complex containing (R,R)-1,2-bis((diisopropylphosphino)amino)cyclohexane in a new coordination form kappa(3)P,P',N-eta(2)-P,N

The syntheses of the chloro complexes [Ru(eta5-C5R5)Cl(L)] (R = H, Me; L = phosphinoamine ligand) (1a-d) have been carried out by reaction of [(eta5-C5H5)RuCl(PPh3)2] or {(eta5-C5Me5)RuCl}4 with the corresponding phosphinoamine (R,R)-1,2-bis((diisopropylphosphino)amino)cyclohexane), R,R-dippach, or 1,2-bis(((diisopropylphosphino)amino)ethane), dippae. The chloride abstraction reactions from these compounds lead to different products depending on the starting chlorocomplex and the reaction conditions. Under argon atmosphere, chloride abstraction from [(eta5-C5Me5)RuCl(R,R-dippach)] with NaBAr'4 yields the compound [(eta5-C5Me5)Ru(kappa3P,P'-(R,R)-dippach)][BAr'4] (2b) which exhibits a three-membered ring Ru-N-P by a new coordination form of this phosphinoamine. However, under the same conditions the reaction starting from [(eta5-C5Me5)RuCl(dippae)] yields the unsaturated 16 electron complex [(eta5-C5Me5)Ru(dippae)][BAr'4] (2d). The bonding modes of R,R-dippach and dippae ligands have been analyzed by DFT calculations. The possibility of tridentate P,N,P-coordination of the phosphinoamide ligand to a fragment [(eta5-C5Me5)Ru]+ is always present, but only the presence of a cyclohexane unit in the ligand framework converts this bonding mode in a more favorable option than the usual P,P-coordination. Dinitrogen [(eta5-C5R5)Ru(N2)(L)][BAr'4] (3a-d) and dioxygen complexes [(eta5-C5H5)Ru(O2)(R,R-dippach)][BPh4] (4a) and [(eta5-C5Me5)Ru(O2)(L)][BPh4] (4b,d) have been prepared by chloride abstraction under dinitrogen or dioxygen atmosphere, respectively. The presence of 16 electron [(eta5-C5H5)Ru(R,R-dippach)]+ species in fluorobenzene solutions of the corresponding dinitrogen or dioxygen complexes in conjunction with the presence of [BAr'4]- gave in some cases a small fraction of [Ru(eta5-C5H5)(eta6-C6H5F)][BAr'4] (5a), which has been isolated and characterized by X-ray diffraction.     

Intramolecular C-H insertion reactions of (eta(5)-cyclopentadienyl)dicarbonyliron carbene complexes: scope of the reactions and application to the synthesis of (+/-)-sterpurene and (+/-)-pentalenene

(eta(5)-Cyclopentadienyl)dicarbonyliron carbene complexes, [(eta(5)-C(5)H(5))(CO)(2)Fe=CHR](+)BF(4)(-), are generated as reactive intermediates from thioether derivatives, (eta(5)-C(5)H(5))(CO)(2)FeCH(R)SPh, by S-alkylation with trimethyloxonium tetrafluoroborate and loss of thioanisole. The carbene complexes undergo intramolecular C-H insertion into appropriately situated side chains to form cyclopentane derivatives. The reaction has been developed into a general procedure employing cycloalkanones as scaffolds bearing the iron carbene moieties and the side chains at C(2) and C(3), respectively. The products of the intramolecular insertion reactions are substituted bicyclo[n.3.0]alkanones. The scope and limitations of the reaction are described. The reaction is applied to a total synthesis of sterpurene and to a formal synthesis of pentalenene. Overall, this approach to cyclopentane annulation complements the related metal-catalyzed insertion reactions of diazocarbonyl compounds, which are also believed to occur via metal carbene complexes.     

Simple syntheses, structural diversity, and Tishchenko reaction catalysis of neutral homoleptic rare earth(II or III) 3,5-di-tert-butylpyrazolates--the structures of

The homoleptic rare-earth pyrazolate complexes [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Sm, Lu), [Eu4(tBu2pz)8] and the mixed oxidation state species [Yb2(tBu2pz)5] (tBu2pz = 3,5-di-tert-butylpyrazolate) have been prepared by a simple reaction between the corresponding rare-earth metal and 3,5-di-tert-butylpyrazole, in the presence of mercury, at elevated temperatures. In addition, [Yb2(tBu2pz)6] was prepared by redox transmetallation/ligand exchange between ytterbium, diphenylmercury(II) and tBu2pzH in toluene, whilst the same reactants in toluene under different conditions or in diethyl ether gave [Yb2(tBu2pz)5]. The complexes of the trivalent lanthanoids display dimeric structures [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu) with chelating eta2-terminal and eta2:eta2-bridging pyrazolate coordination. The considerably smaller Sc3+ ion forms monomeric [Sc(tBu2pz)3] of putative D3h molecular symmetry, with pyrazolate ligands solely eta2-bonded. [Eu4(tBu2pz)8] is a structurally remarkable tetranuclear EuII complex with two types of europium centres in a linear array. The outer two are bonded to one terminal and two bridging pyrazolates, and the inner two are coordinated by four bridging ligands. Unprecedented mu-eta5:eta2 pyrazolate ligation is observed, with each outer Eu2+ sandwiched between two eta5-bonded pyrazolate groups, which are also eta2-linked to an inner Eu2+. The two inner Eu2+ ions are linked together by two equally occupied components of each of two symmetry related, disordered pyrazolate groups with one component eta4:eta2 bridging and one eta3:eta2 bridging. [La2(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates.     

Synthesis and selectivity in the formation of cyclophosphazene-derived 1,3-cyclohexadienes from reactions of RCpCo(COD) [R = MeOC(O)] with alkynes and alkenes

The first examples of mono and bisfluorophosphazene derived [eta (5)-cyclopentadienyl] [eta (4)-1,3-cyclohexadiene] cobalt complexes have been prepared along with the sandwich compound [eta (5)-carbomethoxycyclopentadienyl] [eta (4)-1,3-bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] cobalt and acetylene trimerized products from the reactions of [eta (5)-MeOC(O)C 5H 4]Co[COD], PhCCP 3N 3F 5 and phenylacetylene in the presence or absence of an additional cycloalkene or indene. Formation of these mono and bis fluorophosphazene derived cobalt cyclohexadiene complexes provide experimental evidence for a metallacyclopentadiene pathway for cyclohexadiene formation in CpCo catalyzed reactions. Selectivity is also observed in the formation of bisfluorophosphazene derived cyclohexadienes which stems from the fact that two P 3N 3F 5 units cannot be accommodated on vicinal carbon atoms of a carbacycle or metallacycle. Interestingly, reactions of (beta-phenylethynyl)pentafluorobenzene with [eta (5)-MeOC(O)C 5H 4]Co[COD] in the presence and absence of external cycloalkene under identical reaction conditions yielded only the cis and trans isomers of the metallocene [eta (5)-MeOC(O)C 5H 4]Co[eta (4)-C 4Ph 2(C 6F 5) 2] along with alkyne trimerized product indicating that the selectivity in cyclohexadiene formation is governed more by steric than electronic factors. All the new compounds were characterized by (1)H, (13)C, (31)P, and (19)F NMR as well as mass spectrometry and elemental analysis. Mono and bispentafluorocyclotriphosphazene derived [eta (5)-cyclopentadienyl] [eta (4)-1,3-cyclohexadiene] cobalt complexes and [eta (5)-carbomethoxycyclopentadienyl] [eta (4)-bis(1,3-pentafluorophenyl)-2,4-diphenylcyclobutadiene] cobalt have also been structurally characterized by single crystal X-ray analysis.     

Polynuclear magnesium and magnesium-titanium species. Syntheses and crystal structures of [Mg4(mu3,eta2-ddbfo)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)29eta1-ddbfo2],

Tetranuclear magnesium complexes with chelating alkoxo ligands have been synthesized with the aim of investigating coordinatively unsaturated magnesium sites able to bind TiX4 (X = Cl, OR), of the type necessary for the formation of the active centers in polymerization catalysts. The magnesium compound [Mg4(mu3,eta2-ddbfo)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)2(eta1-ddbfo)2] x 2CH2Cl2 (1) (ddbfo = 2,3-dihydro-2,2-dimethyl-7-benzofuranoxide) was prepared by the reaction of MgBu2 with ddbfoH in dichloromethane. Complex 1 exists as a centrosymmetric tetranuclear species with two different types of magnesium centers corresponding to octahedral MgO6 and trigonal bipyramidal MgO5 geometry. Compound 1 is monoclinic, space group P2(1/c), with a = 12.053(2) A, b = 13.323(3) A, c = 17.069(3) A, beta = 98.50(3) degrees , and Z = 4. The reaction of 1 with methanol in tetrahydrofuran (THF) gave compound [Mg4(mu3-OMe)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)2(eta1-ddbfo)2(CH3OH)5] x CH3OH x THF (2). During this reaction one of the two five-coordinate MgO5 centers in 1 is completed by a methanol molecule and becomes octahedral in 2. Species 2 belongs to the P2(1/n) monoclinic space group, with a = 13.323(3) A, b = 20.768(4) A, c = 27.584(6) A, beta = 104.26(3) degrees , and Z = 4. Compound [Mg4(mu3,eta2-thffo)2(mu,zeta2-thffo)2(mu,eta1-thffo)2[mu-OTi(DIPP)3]2] x 2CH2Cl2 (3) is formed as a result of substitution of two thffo (thffo = 2-tetrahydrofurfuroxide) ligands bonded to the five-coordinate magnesium atom in [Mg4(thffo)8] by bulky OTi(DIPP)3 (DIPP = diisopropylphenolate) groups. Crystals of 3 are monoclinic, space group P2(1/n), with a = 17.069(3) A, b = 18.421(4) A, 17.815(4) A, beta = 90.77(3) degrees , and Z = 4. The X-ray crystal structures of complexes 1-3 are discussed in terms of explaining the role of the coordinatively unsaturated magnesium site in chiral catalyst active center formation.     

Syntheses and characterization of mu,eta(1),eta(1)-3,5-di-tert-butylpyrazolato derivatives of aluminum

The 3,5-di-tert-butylpyrazolato (3,5-tBu(2)pz) derivatives of aluminum [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(1)R(2)](2) (R(1) = R(2) = Me 1; R(1) = R(2) = Et, 2; R(1) = R(2) = Cl, 3; R(1) = R(2) = I, 4; [(eta(2)-3,5-tBu(2)pz)(3)Al], 5; [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)(C triple bond CPh)(2)] (E = S (6), Se (7), Te (8)) have been prepared in good yield. Compounds 1 and 2 were obtained by the reactions of H[3,5-tBu(2)pz] with Me(3)Al and Et(3)Al, respectively. Reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)H(2)](2) with the pyrazole H[3,5-tBu(2)pz] gave [(eta(2)-3,5-tBu(2)pz)(3)Al] (5). The reaction of [(eta(1),eta(1)-3,5-tBu(2)pz)(mu-Al)R(2)](2) (R = H, Me) and I(2) yielded 4, while the reaction of 1 equiv of K[3,5-tBu(2)pz] and AlCl(3) afforded 3. In addition, the reaction of [Al(2)(eta(1),eta(1)-3,5-tBu(2)pz)(2)(mu-E)H(2)] and HC triple bond CPh gave 6, 7, and 8. All compounds have been characterized by elemental analysis, NMR, and mass spectroscopy. The molecular structure analyses of compounds 1, 3, 6, and 7 by X-ray crystallography showed that complexes 1 and 3 are dimeric with two eta(1),eta(1)-pyrazolato groups in twisted conformation while 6 and 7 with two eta(1),eta(1)-pyrazolato groups display a boat conformation.     

Novel hetero-bimetallic metalla-macrocycles based on the bis-1-pyridyl ferrocene [Fe(eta 5-C5H(4)-1-C5H4N)2] ligand. Design,synthesis and structural characterization of the complexes [Fe(eta 5-C5H(4)-1-C5H4N)2](AgI)2(2+)/(CuII)2(4+)/(ZnII)2(4+)

The bidentate sandwich ligand [Fe(eta 5-C5H(4)-1-C5H4N)2] has been prepared, structurally characterized and employed in the preparation of the novel supramolecular heterobimetallic metalla-macrocycles [Fe(eta 5-C5H(4)-1-C5H4N)2]Ag2(NO3)(2).1.5H2O, [Fe(eta 5-C5H(4)-1-C5H4N)2]Cu2(CH3COO)(4).3H2O and [Fe(eta 5-C5H(4)-1-C5H4N)2]Zn2Cl4.     

Ruthenium(II) complexes containing bis(2-(diphenylphosphino)phenyl) ether and their catalytic activity in hydrogenation reactions

The half-sandwich complexes [(eta5-C5H5)RuCl(DPEphos)] (1) and [{(eta6-p-cymene)RuCl2}2(mu-DPEphos)] (2) were synthesized by the reaction of bis(2-(diphenylphosphino)phenyl) ether (DPEphos) with a mixture of ruthenium trichloride trihydrate and cyclopentadiene and with [(eta6-p-cymene)RuCl2]2, respectively. Treatment of DPEphos with cis-[RuCl2(dmso)4] afforded fac-[RuCl2(kappa3-P,O,P-DPEphos)(dmso)] (3). The dmso ligand in 3 can be substituted by pyridine, 2,2'-bipyridine, 4,4'-bipyridine, and PPh3 to yield trans,cis-[RuCl2(DPEphos)(C5H5N)2] (4), cis,cis-[RuCl2(DPEphos)(2,2'-bipyridine)] (5), trans,cis-[RuCl2(DPEphos)(mu-4,4'-bipyridine)]n (6), and mer,trans-[RuCl2(kappa3-P,P,O-DPEphos)(PPh3)] (7), respectively. Refluxing [(eta6-p-cymene)RuCl2]2 with DPEphos in moist acetonitrile leads to the elimination of the p-cymene group and the formation of the octahedral complex cis,cis-[RuCl2(DPEphos)(H2O)(CH3CN)] (8). The structures of the complexes 1-5, 7, and 8 are confirmed by X-ray crystallography. The catalytic activity of these complexes for the hydrogenation of styrene is studied.     

Synthesis, reactivity, and X-ray crystallographic characterization of mono-, di-, and tetranuclear palladium(II)-metalated species

The reactivity of the tetranuclear metallated palladium compound (Pd[mu 2-(C6H4)PPh2]Br)4 (1) with different ligands has been investigated with the aim of evaluating the influence of the entering ligand on the nature of the reaction products. The results confirmed the ability of the ligand [(C6H4)PPh2]- to expand a bridging [mu 2-] or a chelating [eta 2-] coordination mode, depending on the auxiliary ligands present in the complex. Bulky phosphines stabilize mononuclear species of formula (Pd[eta 2-(C6H4)PPh2]Br[P]), with a four-atom metallocycle, while small phosphines give dinuclear compounds. The molecular structures of three different metalated palladium compounds have been determined by single-crystal X-ray crystallography; the tetranuclear (Pd[mu 2-(C6H4)PPh2]Cl)4 (2), the dinuclear(Pd[mu 2-(C6H4)PPh2]Br[PMe3])2 (3), and the mononuclear (Pd[eta 2-(C6H4)PPh2]Br[PCBr]), (PCBr = P(o-BrC6H4)Ph2) (9) were obtained, the first one by halogen exchange reaction and the others by frame degradation of 1.     

Synthesis, Raman spectra and crystal structures of [Cu(XeF2)n](SbF6)2 (n=2, 4)

Pure [Cu(XeF2)2](SbF6)2 was prepared by the reaction of Cu(SbF 6) 2 with a stoichiometric amount of XeF2 in anhydrous hydrogen fluoride (aHF) at ambient temperature. The reaction between Cu(SbF6)2 and XeF2 (1:4 molar ratio) in aHF yielded [Cu(XeF2)4](SbF6)2 contaminated with traces of Xe 2F 3SbF6 and CuF2. The 6-fold coordination of Cu(2+) in [Cu(XeF2)2](SbF6)2 includes two fluorine atoms from two XeF2 ligands and four fluorine atoms provided by four [SbF6](-) anions. The neighboring [Cu(XeF 2)2](2+) moieties are connected via two [SbF6] units, with the bridging fluorine atoms in cis positions, into infinite [Cu(eta(1)-XeF2)2](cis-eta(2)-SbF 6)2[Cu(eta(1)-XeF 2)2] chains. Because of the high electron affinity of Cu(2+), coordinated XeF2 shows the highest distortion (Xe-Fb=210.2(5) pm, Xe-Ft=190.6(5) pm) observed so far among all known [M(x+)(XeF2)n](A)x (A=BF4, PF6, etc.) complexes. The four equatorial coordination sites of the Cu(2+) ion in [Cu(XeF 2) 4](SbF6)2 are occupied by four XeF 2 ligands. Two fluorine atoms belonging to two [SbF6] units complete the Cu (2+) coordination environment. The neighboring [Cu(XeF2)4](2+) species are linked via one [SbF6] unit, with bridging fluorine atoms in trans positions, into linear infinite [Cu(eta(1)-XeF2)4](trans-eta(2)-SbF6)[Cu(eta(1)-XeF2)4] chains. To compensate for the remaining positive charge, crystallographically independent [SbF6](-) anions are located between the chains and are fixed in the crystal space by weak Xe...F(Sb) interactions.     

Novel heteroleptic cis-(C--N)2Pd(II) chelates for the preparation of enantiopure planar chiral cyclopalladated 2-[tricarbonyl(eta6-phenyl)chromium]pyridine

In the presence of large amounts of [Me4N]Cl, the reaction of ortho-chloromercurated 2-[(eta6-phenyl)tricarbonylchromium]pyridine with mu-chloro cyclopalladated aromatic compounds yields a series of new heteroleptic heterodinuclear cis-(C--N)2Pd(II) complexes, which are valuable precursors of planar chiral cyclopalladated (eta6-arene)Cr(CO)3 complexes.     

C-H and P-C(Ph) activation competitive processes caused by interaction with the solvate [cis-Pt(C6F5)2(thf)2

The study of the reaction between the ethylene [Pt(eta-H2C = CH2)(PPh3)2] or alkyne [Pt(eta2-HC [triple bond] CR)(PPh3)2] (R = SiMe3 1, Bu(t) 2) complexes with [cis-Pt(C6F5)2(thf)2] (thf = tetrahydrofuran) has enabled us to observe the existence of competitive processes between the activation of a P-C(Ph) bond on the PPh3 ligand, to give the binuclear derivative [cis-(C6F5)2Pt(mu-Ph)(mu-PPh2)Pt(PPh3)] 3, and the activation of a C-H bond of the unsaturated group, to give the corresponding (mu-hydride)(mu-vinyl) [cis, cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-CH = CH2)Pt(C6F5)2] 4 or (mu-hydride)(mu-alkynyl) [cis,cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-C [triple bond]CR)Pt(C6F5)2] (R = SiMe3 5, Bu(t) 6) compounds, respectively. The monitoring of these reactions by NMR spectroscopy has allowed us to detect several intermediates, and to propose a mechanism for the C-H bond activation. In addition, the structures of the (muo-hydride)(mu-alkynyl) complex 5 and the unprecedented (mu-hydride)(mu-vinyl) derivative 4 have been obtained by X-ray crystallographic analyses.