Atmospheric chemistry of diethyl methylphosphonate, diethyl ethylphosphonate, and triethyl phosphate

Rate constants for the reactions of OH radicals and NO(3) radicals with diethyl methylphosphonate [DEMP, (C(2)H(5)O)(2)P(O)CH(3)], diethyl ethylphosphonate [DEEP, (C(2)H(5)O)(2)P(O)C(2)H(5)], and triethyl phosphate [TEP, (C(2)H(5)O)(3)PO] have been measured at 296 +/- 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10(-11) cm(3) molecule(-1) s(-1)) were as follows: DEMP, 5.78 +/- 0.24; DEEP, 6.45 +/- 0.27; and TEP, 5.44 +/- 0.20. The rate constants obtained for the NO(3) radical reactions (in units of 10(-16) cm(3) molecule(-1) s(-1)) were the following: DEMP, 3.7 +/- 1.1; DEEP, 3.4 +/- 1.4; and TEP, 2.4 +/- 1.4. For the reactions of O(3) with DEMP, DEEP, and TEP, an upper limit to the rate constant of <6 x 10(-20) cm(3) molecule(-1) s(-1) was determined for each compound. Products of the reactions of OH radicals with DEMP, DEEP, and TEP were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEP reaction, gas chromatography with flame ionization detection (GC-FID) and in situ Fourier transform infrared (FT-IR) spectroscopy. The API-MS analyses show that the reactions are analogous, with formation of one major product from each reaction: C(2)H(5)OP(O)(OH)CH(3) from DEMP, C(2)H(5)OP(O)(OH)C(2)H(5) from DEEP, and (C(2)H(5)O)(2)P(O)OH from TEP. The FT-IR and GC-FID analyses showed that the major products (and their molar yields) from the TEP reaction are (C(2)H(5)O)(2)P(O)OH (65-82%, initial), CO(2) (80 +/- 10%), and HCHO (55 +/- 5%), together with lesser yields of CH(3)CHO (11 +/- 2%), CO (11 +/- 3%), CH(3)C(O)OONO(2) (8%), organic nitrates (7%), and acetates (4%). The probable reaction mechanisms are discussed.     

Syntheses and chemistry of hypervalent cyclo-R4Sb4, cyclo-(RSbE)n[R = 2-(Me2NCH2)C6H4, E = O, S] and precursors

The cyclostibane R(4)Sb(4)(1)(R = 2-(Me(2)NCH(2))C(6)H(4)) was synthesized by reduction of RSbCl(2) with Mg in THF or with Na in liquid NH(3). The reaction of 1 with [W(CO)(5)(THF)] gives the stibinidene complex RSb[W(CO)(5)](2)(2). RSbCl(2) and (RSbCl)(2)E [E = O (6), E = S (8)] react with KOH or Na(2)S in toluene/water to give the heterocycles (RSbE)(n)[E = O, n= 3 (3); E = S, n= 2 (4)]. The chalcogeno-bridged compounds of the type (RSbCl)(2)E [E = O (6), E = S (8)] were synthesized by reaction of RSbCl(2) with KOH or Na(2)S in toluene/water, but also by reaction of RSbCl(2) with the heterocycles (RSbE)(n). The compounds (RSbI)(2)O (7) and (RSbBr)(2)S (9) were prepared via halogen-exchange reactions between (RSbCl)(2)E and NaI (E = O) or KBr (E = S) or by reactions between RSbI(2) and KOH or RSbBr(2) and Na(2)S. The reaction of cyclo-(RSbS)(2) with W(CO)(5)(THF) in THF results in trapping of the cis isomer in cyclo-(RSbS)(2)[W(CO)(5)](5). The solution behaviour of the compounds was investigated by (1)H and (13)C NMR spectroscopy. The molecular structures of compounds 1-7 and 9 were determined by single-crystal X-ray diffraction.     

Iminic N-bound iminophosphorano versus nitrilic n-bound iminophosphorano Os(IV) complexes: a new double derivatization of the nitrido ligand

The reactions between trans-[Os(IV)(tpy)(Cl)(2)(NCN)] (1) and PPh(3) and between trans-[Os(IV)(tpy)(Cl)(2)(NPPh(3))](+) (2) and CN(-) provide new examples of double derivatization of the nitrido ligand in an Os(VI)-nitrido complex (Os(VI)N). The nitrilic N-bound product from the first reaction, trans-[Os(II)(tpy)(Cl)(2)(NCNPPh(3))] (3), is the coordination isomer of the first iminic N-bound product from the second reaction, trans-[Os(II)(tpy)(Cl)(2)(N(CN)(PPh(3)))] (4). In CH(3)CN at 45 degrees C, 4 undergoes isomerrization to 3 followed by solvolysis and release of (N-cyano)iminophosphorane, NCNPPh(3). These reactions demonstrate new double derivatization reactions of the nitrido ligand in Os(VI)N with its implied synthetic utility.     

Regulation of geometry around the ruthenium center of bis(2-pyridinecarboxylato) complexes by the nitrosyl moiety: syntheses, structures, and theoretical studies

cis-[Ru(NO)Cl(pyca)(2)] (pyca = 2-pyridinecarboxylato), in which the two pyridyl nitrogen atoms of the two pyca ligands coordinate at the trans position to each other and the two carboxylic oxygen atoms at the trans position to the nitrosyl ligand and the chloro ligand, respectively (type I shown as in Chart 1), reacted with NaOCH(3) to generate cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I). The geometry of this complex was confirmed to be the same as the starting complex by X-ray crystallography: C(13.5)H(13)N(3)O(6.5)Ru; monoclinic, P2(1)/n; a = 8.120(1), b = 16.650(1), c = 11.510(1) A; beta = 99.07(1) degrees; V = 1536.7(2) A(3); Z = 4. The cis-trans geometrical change reaction occurred in the reactions of cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I) in water and alcohol (ROH, R = CH(3), C(2)H(5)) to form [[trans-Ru(NO)(pyca)(2)](2)(H(3)O(2))](+) (type V) and trans-[Ru(NO)(OR)(pyca)(2)] (type V). The reactions of the trans-form complexes, trans-[Ru(NO)(H(2)O)(pyca)(2)](+) (type V) and trans-[Ru(NO)(OCH(3))(pyca)(2)] (type V), with Cl(-) in hydrochloric acid solution afforded the cis-form complex, cis-[Ru(NO)Cl(pyca)(2)] (type I). The favorable geometry of [Ru(NO)X(pyca)(2)](n)(+) depended on the nature of the coexisting ligand X. This conclusion was confirmed by theoretical, synthetic, and structural studies. The mono-pyca-containing nitrosylruthenium complex (C(2)H(5))(4)N[Ru(NO)Cl(3)(pyca)] was synthesized by the reaction of [Ru(NO)Cl(5)](2)(-) with Hpyca and characterized by X-ray structural analysis: C(14)H(24)N(3)O(3)Cl(3)Ru; triclinic, Ponemacr;, a = 7.631(1), b = 9.669(1), c = 13.627(1) A; alpha = 83.05(2), beta = 82.23(1), gamma = 81.94(1) degrees; V = 981.1(1) A(3); Z = 2. The type II complex of cis-[Ru(NO)Cl(pyca)(2)] was synthesized by the reaction of [Ru(NO)Cl(3)(pyca)](-) or [Ru(NO)Cl(5)](2)(-) with Hpyca and isolated by column chromatography. The structure was determined by X-ray structural analysis: C(12)H(8)N(3)O(5)ClRu; monoclinic, P2(1)/n; a = 10.010(1), b = 13.280(1), c = 11.335(1) A; beta = 113.45(1) degrees; V = 1382.4(2) A(3); Z = 4.     

Neodymium alkoxides: synthesis,characterization and their combinations with dialkylmagnesiums as unique systems for polymerization and block copolymerization of ethylene and methyl methacrylate

The synthesis and characterization (NMR and X-ray) of a variety of neodymium alkoxides derived from simple and functionalized tertiary monoalcohols, and their application as inorganic precursors in combination with dialkylmagnesium reagents for ethylene and methyl methacrylate (MMA) (co)polymerization have been investigated. Salt metathesis reactions between NdCl(3) and sodium alkoxides in THF led to the formation of trinuclear complexes [Nd(3)(mu(3)-OR)(2)(mu(2)-OR)(3)(OR)(4)(thf)(2)] with R=tBu (1), tAm (2), while aggregate structure [Nd(12)(OtAm)(26)(HOtAm)(2)Cl(11)Na].(OEt(2))(2) (3) was obtained when the synthesis was performed in Et(2)O. [Nd(3)(mu(3)-OtBu)(2)(mu(2)-OtBu)(3)(OtBu)(4)(HOtBu)(2)] (4), prepared by aminolysis of Nd[N(SiMe(3))(2)](3) in hexane, slowly decomposed in toluene into oxo complex [Nd(5)(mu(5)-O)(mu(3)-OtBu)(4)(mu(2)-OtBu)(4)(OtBu)(5)] (5). Finally, the dimer [Nd(2)(mu(2),eta(2)-OR)(2)(eta(2)-OR)(2)(eta(1)-OR)(2)] (OR=OCMe(2)CH(2)CH(2)OMe) (6) was synthesised by aminolysis reaction from the corresponding gamma-donor-functionalized alcohol. Some of these neodymium alkoxides, in particular homoleptic complex 1, when associated in situ to one equivalent of a dialkylmagnesium, allow the formation of an active catalyst for ethylene polymerization. Under mild conditions (0 degrees C, 1 bar), the latter catalyst system exhibited a moderate activity (5-10 kg mol(-1) h(-1) bar(-1)). Effective transfer reactions were observed in the presence of H(2) or PhSiH(3) and renewal/improvement of activity occurred upon extra addition of dialkylmagnesium. The most outstanding feature of this catalytic system lies in the precipitation of the active "Nd-polyethylenyl" species during the ethylene polymerization course as solid S which could be isolated. This heterogeneity was turned to good account, enabling to achieve heterogeneous solid-gas ethylene polymerization and to prepare diblock PE-PMMA copolymers with high diblock efficiency and high molecular weights (M(n) > 200 000). A catalytic cycle for this unique system is proposed based on the isolation of a transmetallation product (7) from a neodymium alkoxide/dialkylmagnesium combination and NMR studies of the latter.     

Porous anionic, cationic, and neutral metal-carboxylate frameworks constructed from flexible tetrapodal ligands: syntheses, structures, ion-exchanges, and magnetic properties

A series of coordination polymers with anionic, cationic, and neutral metal-carboxylate frameworks have been synthesized by using a flexible tetrapodal ligand tetrakis[4-(carboxyphenyl)oxamethyl] methane acid (H(4)X). The reactions between divalent transition-metal ions and H(4)X ligands gave [M(3)X(2)]·[NH(2)(CH(3))(2)](2)·8DMA (M = Co (1), Mn (2), Cd(3)) which have anionic metal-carboxylate frameworks with NH(2)(CH(3))(2)(+) cations filled in channels. The reactions of trivalent metal ions Y(III), Dy(III), and In(III) with H(4)X ligands afforded cationic metal-carboxylate frameworks [M(3)X(2)·(NO(3))·(DMA)(2)·(H(2)O)]·5DMA·2H(2)O (M = Y(4), Dy(5)) and [In(2)X·(OH)(2)]·3DMA·6H(2)O (6) with the NO(3)(-) and OH(-) serving as counterions, respectively. Moreover, a neutral metal-carboxylate framework [Pb(2)X·(DMA)(2)]·2DMA (7) can also be isolated from reaction of Pb(II) and H(4)X ligands. The charged metal-carboxylate frameworks 1-5 have selectivity for specific counterions in the reaction system, and compounds 1 and 2 display ion-exchange behavior. Moreover, magnetic property measurements on compounds 1, 2, and 5 indicate that there exists weak antiferromagnetic interactions between magnetic centers in the three compounds.     

Synthesis and properties of rhenium carbonyl complexes of alpha,alpha'-bis[(1-pyrenyl)pyrazol-1-yl]alkane ligands

The reaction between (1-acetyl)pyrene and dimethylformamide dimethylacetal followed by condensation of the resulting product mixture with hydrazine affords 3(5)-(1-pyrenyl)pyrazole (2) in good yield. The easily separable bis[(1-pyrenyl)pyrazole]methane derivatives CH(2)(3-pz(pyrene))(2) (3a, pz = pyrazolyl ring) and CH(2)(3-pz(pyrene))(5-pz(pyrene)) (3b) were prepared by metathetical reactions between pyrazole and CH(2)Cl(2), while CH((n)()Pr)(pz(pyrene))(2) (4) was prepared by transamination of 2 with butyraldehyde diethylacetal. Compounds 2-4 are luminescent under irradiation with UV light and have pyrenyl monomer-based emissions centered near 400 nm. Compounds 3a and 4 each react with Re(CO)(5)Br in a 1:1 molar ratio to form highly insoluble complexes Re(CO)(3)Br[(pz(pyrene))(2)CH(2)] (5) and Re(CO)(3)Br[(pz(pyrene))(2)CH((n)()Pr)] (6). Complex Re(CO)(3)Br[(pz)(2)CMe(2)] (7) was also prepared. X-ray structural studies of 6 show extensive pi-stacking of pyrenyl groups to form two-dimensional sheets. Pulsed field gradient spin-echo NMR (PGSE-NMR) experiments show that the complexes are monomeric in tetrachloroethane. Variable-temperature, difference NOE and 2-D NMR experiments demonstrate that isomers are present in solution that differ by restricted rotation about the pyrazolyl-pyrenyl bond. The pyrenyl-based emissions centered near 400 nm are quenched by complexation to the Re(CO)(3)Br moiety in 5 and 6.     

Reactivity and selectivity of the N-acetyl-Glu-P-1, N-acetyl-Glu-P-2, N-acetyl-MeIQx,and N-acetyl-IQx nitrenium ions: comparison to carbocyclic N-arylnitrenium ions

The model ultimate carcinogens 1a-d, related to the metabolites of the food-derived carcinogenic heterocyclic amines Glu-P-1, Glu-P-2, MeIQx, and IQx, spontaneously decompose in neutral aqueous solution to generate the heterocyclic nitrenium ions, 2a-d. The less reactive esters 1a and 1b also undergo acid-catalyzed ester hydrolysis to generate the corresponding hydroxamic acids at pH <2, while the more reactive 2c and 2d are prone to rearrangement in nonaqueous solvents. The reactions of the nitrenium ions with AcO(-), HPO(4)(2-), N(3)(-), and 2'-deoxyguanosine (d-G) were characterized in aqueous solution by using a combination of competitive trapping methods and product isolation and identification. The reactions with N(3)(-) and d-G generally follow patterns previously established for carbocyclic nitrenium ions, but the reactions with AcO(-) and HPO(4)(2-) are unusual. Similar reactions have previously only been reported for heterocyclic 1-alkyl-2-imidazolium ions. The N(3)(-)/solvent selectivities of these ions (5.1 x 10(6) M(-1) for 2a, 2.3 x 10(6) M(-1) for 2b, 1.2 x 10(5) M(-1) for 2c, and 5.2 x 10(4) M(-1) for 2d) are comparable to those of highly selective carbocyclic nitrenium ions. If k(az) for these ions is diffusion limited at ca. 5 x 10(9) M(-1) s(-1) the aqueous solution lifetimes of these ions range from 10 micros (2d) to 1 ms (2a). These ions are also highly selective for trapping by d-G, but comparisons to other nitrenium ions show that they are 10- to 50-fold less selective for trapping by d-G than they would be if both the N(3)(-) and d-G reactions were diffusion limited. This is not a consequence of their heterocyclic structures. Several carbocyclic ions show similar behavior. The relatively inefficient trapping of 2c and 2d by d-G may account for the observation of the unusual minor N-2 d-G adduct that is isolated for both of these nitrenium ions, but has not previously been observed for the reactions of other nitrenium ions with monomeric d-G.     

Molybdenum amido complexes with single Mo-N bonds: synthesis,structure, and reactivity

Reactions of the complex [MoCl(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1) (phen=1,10-phenanthroline) with potassium arylamides were used to synthesize the amido complexes [Mo(N(R)Ar)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (R=H, Ar=Ph, 2 a; R=H, Ar=p-tolyl, 2 b; R=Me, Ar=Ph; 2 c). For 2 b the Mo-N(amido) bond length (2.105(4) A) is consistent with it being a single bond, with which the metal attains an 18-electron configuration. The reaction of 2 b with HOTf affords the amino complex [Mo(eta(3)-C(3)H(4)-Me-2)(NH(2)(p-tol))(CO)(2)(phen)]OTf (3-OTf). Treatment of 3-OTf with nBuLi or KN(SiMe(3))(2) regenerates 2 b. The new amido complexes react with CS(2), arylisothiocyanates and maleic anhydride. A single product corresponding to the formal insertion of the electrophile into the Mo-N(amido) bond is obtained in each case. For maleic anhydride, ring opening accompanied the formation of the insertion product. The reaction of 2 b with maleimide affords [Mo(eta(3)-C(3)H(4)-Me-2)[NC(O)CH=CHC(O)](CO)(2)(phen)] (7), which results from simple acid-base metathesis. The reaction of 2 b with (p-tol)NCO affords [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(eta(2)-MoO(4))] (8), which corresponds to oxidation of one third of the metal atoms to Mo(VI). Complex 8 was also obtained in the reactions of 2 b with CO(2) or the lactide 3,6-dimethyl-1,4-dioxane-2,5-dione. The structures of the compounds 2 b, 3-OTf, [Mo(eta(3)-C(3)H(4)-Me-2)[SC(S)(N(H)Ph)](CO)(2)(phen)] (4), [Mo(eta(3)-C(3)H(4)-Me-2)[SC(N(p-tol))(NH(p-tol))](CO)(2)(phen)] (5 a), and [Mo(eta(3)-C(3)H(4)-Me-2)[OC(O)CH=CHC(O)(NH(p-tol))](CO)(2)(phen)] (6), 7, and 8 (both the free complex and its N,N'-di(p-tolyl)urea adduct) were determined by X-ray diffraction.     

Reaction chemistry of complexes containing Pt--H, Pt--SH, or Pt--S fragments: from their apparent simplicity to the maze of reactions underlying their interconversion

The relevance of platinum in the reaction of thiophene and derivatives with homogeneous transition-metal complexes as models for hydrodesulfurization has led us to the study of the reaction chemistry of complexes containing Pt--H, Pt--SH, and Pt--S fragments. Exploration of the reactions triggered by addition of controlled amounts of Na2S or NaSH to [Pt2(H)2(mu-H)(dppp)2]ClO4 (1) has provided evidence of the formation of complexes [Pt2(mu-H)(mu-S)(dppp)2]ClO4 (2), [Pt(H)(SH)(dppp)] (3), [Pt2(mu-S)2(dppp)2] (4), [Pt2(mu-S)(dppp)2] (5) and [Pt(SH)2(dppp)], in which dppp denotes 1,3-bis(diphenylphosphanyl)propane. Consequently, complexes 1, 2, and 5 as well as the already reported 3, 4, and [Pt(SH)2(dppp)] have been obtained and fully characterized spectroscopically. Also the crystal structures of 1 and 2 have been solved. Complexes 1-5 constitute the main framework of the network of reactions that account for the evolution of 1 under various experimental conditions as shown in Scheme 1. Apparently, this network has complexes 2 and 4 as dead-ends. However, their reciprocal interconversion by means of the replacement of one bridging hydride or sulfide ligand in the respective {Pt(mu-H)(mu-S)Pt} and {Pt(mu-S)2Pt} cores enables the closure of the reaction cycle involving complexes 1-5. Theoretical calculations support the existence of the undetected intermediates proposed for conversion from 1 to 2 and from 3 to 2 and also account for the fluxional behavior of 1 in solution. The intermediates proposed are consistent with the experimental results obtained in comparable reactions carried out with labeled reagents, which have provided evidence that complex 1 is the source of the hydride ligands in complexes 2 and 3. Overall, our results show the strong dependence on the experimental conditions for the formation of complexes 1-5 as well as for their further conversion in solution.     

Synthesis of [Ag(NH=CMe(2))(2)]ClO(4) and its use as a source of acetimine. 1. Synthesis of the first acetimine rhodium complexes and the first crystal structure of a diacetonamine complex

The reaction of AgClO(4) and NH(3) in acetone gave [Ag(NH=CMe(2))(2)]ClO(4) (1). The reactions of 1 with [RhCl(diolefin)](2) or [RhCl(CO)(2)](2) (2:1) gave the bis(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(2)]ClO(4) [diolefin = 1,5 cyclooctadiene = cod (2), norbornadiene = nbd (3)] or [Rh(CO)(2)(NH=CMe(2))(2)]ClO(4) (4), respectively. Mono(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(PPh(3))]ClO(4) [diolefin = cod (5), nbd (6)] or [RhCl(diolefin)(NH=CMe(2))] [diolefin = cod (7), nbd (8)] were obtained by reacting 2 or 3 with PPh(3) (1:1) or with Me(4)NCl (1:1.1), respectively. The reaction of 4 with PR(3) (R = Ph, To, molar ratio 1:2) led to [Rh(CO)(NH=CMe(2))(PR(3))(2)]ClO(4) [R = Ph (9), C(6)H(4)Me-4 = To (10)] while cis-[Rh(CO)(NH=CMe(2))(2)(PPh(3))]ClO(4) (11) was isolated from the reaction of 1 with [RhCl(CO)(PPh(3))](2) (1:1). The crystal structures of 5 and [Ag[H(2)NC(Me)(2)CH(2)C(O)Me](PTo(3))]ClO(4) (A), a product obtained in a reaction between NH(3), AgClO(4), and PTo(3), have been determined.     

Carbonylchromium derivatives of bismuth: new syntheses and relevance to cbond;o activation

We have discovered a series of novel pentacarbonylchromium derivatives of bismuth from the reactions of NaBiO(3) with [Cr(CO)(6)] in KOH/MeOH solutions. When the reaction was carried out at room temperature, the highly charged [Bi[Cr(CO)(5)](4)](3-) (1) was obtained, whose structure was shown by X-ray analysis to possess a central bismuth atom tetrahedrally coordinated to four [Cr(CO)(5)] groups. As the reaction was heated at 80 degrees C, the methyl-substituted complex [MeBi[Cr(CO)(5)](3)](2-)(2) was obtained, presumably via the CbondO activation of MeOH. Further reactions of 1 with CH(2)Cl(2) or CHtbondCCH(2)Br form the halo-substituted complexes [XBi[Cr(CO)(5)](3)](2-)(X=Cl, 3; Br, 4), respectively. On the other hand, the reactions of 1 with RI (R=Me, Et) led to the formation of the alkyl-substituted complexes [RBi[Cr(CO)(5)](3)](2-)(R=Me, 2; Et). The formation of complexes 1-4 is discussed, presumably via the intermediate bismuthinidene [Bi[Cr(CO)(5)](3)](-) or the trianion [Bi[Cr(CO)(5)](3)](3-).     

Photoinduced Fe-Cp bond cleavage and insertion reactions of strained silicon- and sulphur-bridged [1]ferrocenophanes in the presence of transition-metal carbonyls

The photochemical reactions of the moderately strained sila[1]ferrocenophane [Fe(eta-C(5)H(4))(2)SiPh(2)] (1) and the highly strained thia[1]ferrocenophane [Fe(eta-C(5)H(4))(2)S] (8) with transition-metal carbonyls ([Fe(CO)(5)], [Fe(2)(CO)(9)] and [Co(2)(CO)(8)]) have been studied. The use of metal carbonyls has allowed the products of photochemically induced Fe-cyclopentadienyl (Cp) bond cleavage reactions in the [1]ferrocenophanes to be trapped as stable, characterisable products. During the course of these studies the synthesis of 8 from [Fe(eta-C(5)H(4)Li)(2)TMEDA] (TMEDA=N,N,N',N'-tetramethylethylenediamine) and S(SO(2)Ph)(2) has been significantly improved by a change of reaction solvent and temperature. Photochemical reaction of 1 with excess [Fe(CO)(5)] in THF gave the dinuclear complex [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)SiPh(2)] (9). The analogous photolytic reaction of 8 with [Fe(CO)(5)] in THF gave cyclic dimer [Fe(eta-C(5)H(4))(2)S](2) (10) and [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)S] (11), with the former being the major product. Photolysis of 1 with [Co(2)(CO)(8)] afforded the remarkable tetrametallic dimer [(CO)(2)Co(eta-C(5)H(4))SiPh(2)(eta-C(5)H(4))Fe(CO)(2)](2) (13). The corresponding photochemical reaction of 8 with [Co(2)(CO)(8)] gave a trimetallic insertion product in high conversion, [Co(CO)(4)(CO)(2)Fe(eta-C(5)H(4))S(eta-C(5)H(4))Co(CO)(2)] (14). These reactivity studies show that UV light promotes Fe-Cp bond cleavage reactions of both of the [1]ferrocenophanes 1 and 8. We have found that, whereas the less strained sila[1]ferrocenophane 1 requires photoactivation for Fe-Cp bond insertions to occur, the highly strained thia[1]ferrocenophane 8 undergoes both irradiative and non-irradiative insertions, although the latter occur at a slower rate. Our results suggest that such photoinduced bond cleavage reactions may be general and applicable to other related strained organometallic rings with pi-hydrocarbon ligands.     

Synthesis and characterization of nickel inverse 9-metallacrown-3, palladium-silver, and dinuclear platinum complexes containing pyrazole-functionalized NHC ligands

Three metallacrown nickel complexes [Ni(3)(μ-OH)(L1)(3)](PF(6))(2) (1, L1 = 3-((N-methylimidazolylidenyl)methyl)-5-methylpyrazolate), [Ni(3)(μ-OH)(L2)(3)](PF(6))(2) (2, L2 = 3-((N-mesitylimidazolylidenyl)methyl)-5-methylpyrazolate), and [Ni(3)(μ-OH)(L3)(3)](PF(6))(2) (3, L3 = 3-((N-pyrimidin-2-ylimidazolylidenyl)methyl)-5-methylpyrazolate) were obtained by the reactions of corresponding silver-NHC complexes with Raney nickel powder at 45 °C. The same reaction at 80 °C afforded [Ni(3)(L2)(4)](PF(6))(2) (4). The carbene-transfer reaction of the silver-carbene complex with [(η(3)-C(3)H(5))PdCl](2) yielded the heterotrimetallic complex [AgPd(2)(η(3)-C(3)H(5))(2)(L2)(2)](PF(6)) (5), whereas the carbene-transfer reaction with Pt(cod)Cl(2) gave [Pt(2)(L3)(2)](PF(6))(2) (6). All of these complexes have been fully characterized by ESI-MS, NMR spectroscopy, and elemental analysis. The molecular structures of 1-6 were also studied by X-ray diffraction analysis. In 1-3, three nickel centers are bridged together by three pyrazole-NHC ligands and a hydroxide group, forming a 9-metallacrown-3 topology. Complex 4 is paramagnetic, consisting of two square-planar nickel(II) ions and one tetrahedral nickel ion in which three Ni ions are bridged by four pyrazolate units. In the mixed Pd-Ag complex 5, two palladium and one silver centers are bridged by two pyrazole-NHC ligands. Complex 5 showed good catalytic activity in the Sonogashira coupling reaction of aryl bromides and phenylacetylene under mild conditions typically catalyzed by Pd-Cu systems.     

Scope and mechanistic study of the ruthenium-catalyzed ortho-C-H bond activation and cyclization reactions of arylamines with terminal alkynes

The cationic ruthenium hydride complex [(PCy(3))(2)(CO)(CH(3)CN)(2)RuH](+)BF(4)(-) was found to be a highly effective catalyst for the C-H bond activation reaction of arylamines and terminal alkynes. The regioselective catalytic synthesis of substituted quinoline and quinoxaline derivatives was achieved from the ortho-C-H bond activation reaction of arylamines and terminal alkynes by using the catalyst Ru(3)(CO)(12)/HBF(4).OEt(2). The normal isotope effect (k(CH)/k(CD) = 2.5) was observed for the reaction of C(6)H(5)NH(2) and C(6)D(5)NH(2) with propyne. A highly negative Hammett value (rho = -4.4) was obtained from the correlation of the relative rates from a series of meta-substituted anilines, m-XC(6)H(4)NH(2), with sigma(p) in the presence of Ru(3)(CO)(12)/HBF(4).OEt(2) (3 mol % Ru, 1:3 molar ratio). The deuterium labeling studies from the reactions of both indoline and acyclic arylamines with DCCPh showed that the alkyne C-H bond activation step is reversible. The crossover experiment from the reaction of 1-(2-amino-1-phenyl)pyrrole with DCCPh and HCCC(6)H(4)-p-OMe led to preferential deuterium incorporation to the phenyl-substituted quinoline product. A mechanism involving rate-determining ortho-C-H bond activation and intramolecular C-N bond formation steps via an unsaturated cationic ruthenium acetylide complex has been proposed.     

Insights into the metathesis reaction involving M-M,C-C,and M-C triple bonds from computations employing density functional theory on model compounds M2(OH)6 and M2(SH)6, where M = Mo and W

Calculations employing density functional theory (Gaussian 98, B3LYP, LANL2DZ, 6-31G) have been undertaken to interrogate the factors influencing the metathesis reaction involving M-M, C-C, and M-C triple bonds for the model compounds M(2)(EH)(6), M(2)(EH)(6)(mu-C(2)H(2)), and [(HE)(3)M(tbd1;CH)](2), where M = Mo, W and E = O, S. Whereas in all cases the ethyne adducts are predicted to be enthalpically favored in the reactions between M(2)(EH)(6) compounds and ethyne, only when M = W and E = O is the alkylidyne product [(HO)(3)W(tbd1;CH)](2) predicted to be more stable than the alkyne adduct. For the reaction M(2)(EH)(6)(mu-C(2)H(2)) --> [(HE)(3)M(tbd1;CH)](2), the deltaG degrees values (kcal mol(-)(1)) are -6 (M = W, E = O), +5 (M = Mo, E = O), +18 (M = W, E = S), and +21 (M = Mo, E = S) and the free energies of activation are calculated to be deltaG() = +19 kcal mol(-)(1) (M = W, E = O) and +34 kcal mol(-)(1) (M = Mo, E = O), where the transition state involves an asymmetric bridged structure M(2)(OH)(4)(mu-OH)(2)(CH)(mu-CH) in which the C-C bond has broken; C.C = 1.89 and 1.98 A for W and Mo, respectively. These results are discussed in terms of the experimental observations of the reactions involving ethyne and the symmetrically substituted alkynes (RCCR, where R = Me, Et) with M(2)(O(t)()Bu)(6) and M(2)(O(t)()Bu)(2)(S(t)()Bu)(4) compounds, where M = Mo, W.     

Germyl- and germylene-bridged complexes of Rh/Ir and subsequent chemistry of a bridging germylene group

A series of neutral and cationic germylene-bridged complexes and a neutral germyl(germylene) complex have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Reaction of 1 equiv of primary germanes, RGeH(3) (R = Ph, (t)Bu), with [RhIr(CO)(3)(dppm)(2)] (1) at low-temperature yields [RhIr(GeH(2)R)(H)(CO)(3)(dppm)(2)] (R = Ph (3) or (t)Bu (4)), the products of single Ge-H bond activation, which upon warming transform to the germylene-bridged dihydrides, [RhIr(H)(2)(CO)(2)(μ-GeHR)(dppm)(2)] (R = Ph (5) or (t)Bu (6)) by activation of a second Ge-H bond accompanied by CO loss. Both classes of compounds have the diphosphines folded back in a "cradle-shaped" geometry. Although compound 5 reacts with additional phenylgermane at -40 °C to give a germylene-bridged/germyl product, [RhIr(GeH(2)Ph)(H)(2)(CO)(2)(κ(1)-dppm)(μ-GeHPh)(μ-H)(dppm)] (7), warming results in decomposition. However, reaction of 5 with 1 equiv of diphenylgermane at ambient temperature results in a novel mixed bis(μ-germylene) complex, [RhIr(CO)(2)(μ-GeHPh)(μ-GePh(2))(dppm)(2)] (8), containing both mono- and disubstituted germylene fragments. Reaction of 1 equiv of diphenylgermane with complex 1 produces a similar monogermylene-bridged product, [RhIr(H)(2)(CO)(2)(μ-GePh(2))(dppm)(2)] (9), while reaction of 1 with 2 equiv of diphenylgermane yields the germyl/germylene product [RhIr(H)(GeHPh(2))(CO)(3)(κ(1)-dppm)(μ-GePh(2))(dppm)] (10). The above reactions, incorporating first one and then a second equivalent of primary and secondary germanes, were studied by low-temperature multinuclear NMR spectroscopy, revealing details about the stepwise activations of multiple Ge-H bonds. Reaction of diphenylgermane with the cationic complex [RhIr(CH(3))(CO)(2)(dppm)(2)][CF(3)SO(3)] (2) leads to a cationic A-frame-type germylene- and hydride-bridged product, [RhIr(CO)(2)(μ-H)(μ-GePh(2))(dppm)(2)][CF(3)SO(3)] (3), which reversibly activates H(2), yielding a germyl-bridged dihydride and reacts stoichiometrically with water, methanol, and HCl to yield the respective germanol, germamethoxy, and germylchloride products.     

Divergent pathways of C-H bond activation: reactions of (t-Bu(3)PN)(2)TiMe(2) with trimethylaluminum

The reaction of AlMe(3) with (t-Bu(3)PN)(2)TiMe(2) 1 proceeds via competitive reactions of metathesis and C-H activation leading ultimately to two Ti complexes: [(mu(2)-t-Bu(3)PN)Ti(mu-Me)(mu(4)-C)(AlMe(2))(2)](2) 2, [(t-Bu(3)PN)Ti(mu(2)-t-Bu(3)PN)(mu(3)-CH(2))(2)(AlMe(2))(2)(AlMe(3))] 3, and the byproduct (Me(2)Al)(2)(mu-CH(3))(mu-NP(t-Bu(3))) 4. X-ray structural data for 2 and 3 are reported. Compound 3 undergoes thermolysis to generate a new species [Ti(mu(2)-t-Bu(3)PN)(2)(mu(3)-CH(2))(mu(3)-CH)(AlMe(2))(3)] 5. Monitoring of the reaction of 1 with AlMe(3) by (31)P[(1)H] NMR spectroscopy revealed intermediates including (t-Bu(3)PN)TiMe(3) 6. Compound 6 was shown to react with AlMe(3) to give 2 exclusively. Kinetic studies revealed that the sequence of reactions from 6 to 2 involves an initial C-H activation that is a second-order reaction, dependent on the concentration of Ti and Al. The second-order rate constant k(1) was 3.9(5) x 10(-4) M(-1) s(-1) (DeltaH(#) = 63(2) kJ/mol, DeltaS(#) = -80(6) J/mol x K). The rate constants for the subsequent C-H activations leading to 2 were determined to be k(2) = 1.4(2) x 10(-3) s(-1) and k(3) = 7(1) x 10(-3) s(-1). Returning to the more complex reaction of 1, the rate constant for the ligand metathesis affording 4 and 6 was k(met) = 6.1(5) x 10(-5) s(-1) (DeltaH(#) = 37(3) kJ/mol, DeltaS(#) = -203(9) J/mol x K). The concurrent reaction of 1 leading to 3 was found to proceed with a rate constant of k(obs) of 6(1) x 10(-5) s(-1) (DeltaH(#) = 62(5) kJ/mol, DeltaS(#)= -118(17) J/mol x K). Using these kinetic data for these reactions, a stochastic kinetic model was used to compute the concentration profiles of the products and several intermediates with time for reactions using between 10 and 27 equivalents of AlMe(3). These models support the view that equilibrium between 1 x AlMe(3) and 1 x (AlMe(3))(2) accounts for varying product ratios with the concentration of AlMe(3). In a similar vein, similar equilibria account for the transient concentrations of 6 and an intermediate en route to 3. The implications of these reactions and kinetic and thermodynamic data for both C-H bond activation and deactivation pathways for Ti-phosphinimide olefin polymerization catalysts are considered and discussed.     

Quantum yields of the initiation step and chain propagation turnovers in S(RN)1 reactions: photostimulated reaction of 1-iodo-2-methyl-2-phenyl propane with carbanions in DMSO

Neophyl radicals were generated by photoinduced electron transfer (PET) from a suitable donor to the neophyl iodide (1, 1-iodo-2-methyl-2-phenylpropane). The PET reaction of 1 with the enolate anion of cyclohexenone (2) afforded mainly the reduction products tert-butylbenzene (5) and the rearranged isobutylbenzene (6), arising from hydrogen abstraction of the neophyl radical (15) and the rearranged radical 16 intermediates, respectively. The photostimulated reaction of 1 with 2 in the presence of di-tert-butylnitroxide, as a radical trap, afforded adduct 10 in 57% yield. The photoinduced reaction of the enolate anion of acetophenone (3) with 1 gave the substitution products 11 (50%) and 12 (16%), which arise from the coupling of 3 with radicals 15 and 16, respectively. The rate constant obtained for the addition of anion 3 to radical 15 was 1.2 x 10(5) M(-)(1) s(-)(1), by the use of the rearrangement of this radical as a clock reaction. The anion of nitromethane (4) was almost unreactive at the initiation step, but in the presence of 2 under irradiation, it gave high yields (67%) of the substitution product 13 and only 2% of the rearranged product 14. When the ratio of 4 to 1 was diminished, it was possible to observe both substitution products 13 and 14 in 16% and 6.4% yields, respectively. These last results allowed us to estimate the coupling rate constant of neophyl radicals 15 with anion 4 to be at least of the order of 10(6) M(-)(1) s(-)(1). Although the overall quantum yield determined (lambda = 350 nm) for the studied reactions is below 1, the chain lengths (Phi(propagation)) for the reaction of 1 with anions 3 and 4 are 127 and 2, respectively.     

Preparative and structural studies on the carbonyl cyanides of iron, manganese, and ruthenium: fundamentals relevant to the hydrogenases

The reaction of cyanide, carbon monoxide, and ferrous derivatives led to the isolation of three products, trans- and cis-[Fe(CN)(4)(CO)(2)](2)(-) and [Fe(CN)(5)(CO)](3)(-), the first two of which were characterized by single-crystal X-ray diffraction. The new compounds show self-consistent IR, (13)C NMR, and mass spectroscopic properties. The reaction of trans-[Fe(CN)(4)(CO)(2)](2)(-) with Et(4)NCN gives [Fe(CN)(5)(CO)](3)(-) via a first-order (dissociative) pathway. The corresponding cyanation of cis-[Fe(CN)(4)(CO)(2)](2)(-), which is a minor product of the Fe(II)/CN(-)/CO reaction, does not proceed at measurable rates. Methylation of [Fe(CN)(5)(CO)](3)(-) gave exclusively cis-[Fe(CN)(4)(CNMe)(CO)](2)(-), demonstrating the enhanced nucleophilicity of CN(-) trans to CN(-) vs. CN(-) trans to CO. Methylation has an electronic effect similar to that of protonation as determined electrochemically. We also characterized [M(CN)(3)(CO)(3)](n)(-) for Ru (n = 1) and Mn (n = 2) derivatives. The Ru complex, which is new, was prepared by cyanation of a [RuCl(2)(CO)(3)](2) solution.