Andrew Wojcicki

Insertion Reactions of Transition Metal-Carbon σ-Bonded Compounds I: Carbon Monoxide Insertion

Publisher Summary This chapter focuses on the insertion of carbon monoxide (CO) into transition metal–carbon σ bonds. An attempt is made at a complete literature coverage of the insertion of CO. Numerous organometallic reactions conform to the general equation M–X + Y → M–Y–X, where M is a metal and X and Y are monatomic or polyatomic species. Such processes are termed as “insertion reactions.” The chapter also compares relative reactivities and the activation parameters for the CO insertion of various types of metal alkyls. The elimination of carbon monoxide accompanied by the conversion of an acyl group to the corresponding alkyl moiety has been termed as “decarbonylation.” This is the most extensively, as well as intensively, studied type of decarbonylation. The ultraviolet light-induced decarbonylation has been successfully effected in several types of transition metal acyls. In some instances, the decarbonylation can be effected, under mild conditions, using a stoichiometric amount of a CO-abstracting metal complex. The intramolecular nature of carbon monoxide insertion is demonstrated by the ability of ligands (L) other than CO to convert an alkyl metal carbonyl to the corresponding acyl complex.

Insertion Reactions of Transition Metal–Carbon σ-Bonded Compounds II. Sulfur Dioxide and Other Molecules

Publisher Summary This chapter focuses the insertion reactions of transition metal–carbon σ–bonded compounds and presents the insertion and elimination reactions of sulfur dioxide and of a few other unsaturated molecules. The reactions of sulfur dioxide are accorded a complete literature coverage, whereas those of the other inserting species are treated selectively. The metal–carbon σ–bonded compounds of the main group elements are discussed in the context of comparisons with their transition-metal analogs. Assignment of a structure to the SO 2 insertion products is generally made on the basis of infrared and proton nuclear magnetic resonance (NMR) spectroscopic criteria. Kinetic studies on the sulfur dioxide insertion have been few and most have utilized liquid SO 2 as the reaction medium. The effect of the aryl group on the rate of the insertion has been investigated only for CpFe(CO) 2 R in neat SO 2 . Replacement of carbon monoxide (or another attendant ligand) with a stronger base invariably enhances the rate of the SO 2 insertion of a metal alkyl. The reactions that proceed very rapidly, and often exothermally, in liquid SO 2 can be controlled by the use of an organic solvent. The only complex whose kinetic behavior toward the insertion has been examined closely in several solvents is CpFe(CO) 2 (i–Pr). Stereochemical changes occurring at the metal have been investigated for the iron alkyl. The nature of the metal together with its ancillary ligands plays a major role in determining whether the insertion occurs with or without rearrangement.

Studies on substitution, insertion and decarbonylation reactions of some cyclopentadienyliron complexes with phosphorus donor ligands

Abstract The phosphite complexes C 5 H 5 Fe(CO)[P(OR) 3 ]CH 3 (R=CH 3 , n-C4H9 or C 6 H 5 ) have been synthesized by the interaction of C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]CH 3 with P(OR) 3 in tetrahydrofuran at reflux. They react readily with liquid SO2 to afford the corresponding S-sulfinates, C 5 H 5 Fe(CO)[P(OR) 3 ](SO2CH 3 ). The reaction between C 5 H 5 Fe(CO)2CH 3 and P(C 6 H 5 ) 3 in hydrocarbon solvents at reflux yields initially C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ](COCH 3 ), which then undergoes decarbonylation to C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]CH 3 . However, in refluxing dioxane, C 5 H 5 Fe(CO) [P(C 6 Hs) 3 ] (COCH 3 ) has been obtained as the only major carbonyl product. The corresponding dicarbonyl ethyl complex, C 5 H 5 Fe(CO)2C2H 5 , reacts with P(C 6 H 5 ) 3 in heptane at reflux to give C 5 H 5 Fe(CO)[P(C 6 Hs) 3 ] (COC2H 5 ) and C 5 H 5 Fe(CO) [P(C 6 H 5 ) 3 ] Cl. The chloride has been shown to arise from the reaction of CHCI 3 with C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]H, which results from loss of ethylene by C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]C2H 5 . Photochemical reactions between C 5 H 5 Fe(CO)2C2H 5 and P(C 6 H 5 ) 3 in petroleum ether yield C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]C2H 5 directly, without the intermediacy of C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ] (COC2H 5 ). Contrary to a previous report, ultraviolet irradiation of C 5 H 5 Fe(CO)[P(C 6 H 6 ) 3 ](COR) (R = CH 3 or C 5 H 5 ) in hydrocarbon solvents under several different conditions affords the corresponding C 5 H 5 Fe(CO)[P(C 6 H 5 ) 3 ]R in moderate to good yields.

Allenyls and propargyls: versatile ligands in transition-metal chemistry

Abstract Mononuclear, binuclear, and trinuclear transition-metal allenyl and/or propargyl complexes are reviewed with respect to methods of synthesis, structure, and reaction chemistry. Structural relationships among the various types of complexes are presented and, to the extent possible, used to rationalize some patterns of reactivity. Recent developments in the field are accorded special emphasis.

Reactions of coordinated propargyl and allene ligands in cyclopentadienyliron dicarbonyl complexes

Abstract Reactions of η5-C5H5Fe(CO)2CH2CCR (R  CH3, C6H5, and CH2Fe(CO)2(η5-C5H5)) with HBF4 in acetic anhydride yield [η5-C5H5Fe(CO)2(η2CH2CCHR)]+BF−4. The resultant cationic iron-η2-allene complexes react with a wide range of nucleophiles (Nu) to give the following types of behavior: (a) addition of Nu to carbon-1 of the η2-allene fragment (with NaBH4, (C2H5)2NH, and P(C6H5)3, inter alia), (b) addition of Nu to carbon-2 of the η2-allene fragment (with NaOCH3), (c) addition of Nu to the carbonyl carbon (with NaOC2H5), (d) deprotonation of the iron-η2-allene cation to the parent propargylic complex (with N(C2H5)3), and (e) nonselective reactions to yield a mixture of products (with CH3Li). Of these, the most common is behavior (a); together with the protonation of η5-C5H5Fe(CO)2CH2CCR it stimulates the two-step (3 + 2) cycloaddition reactions between electrophilic molecules and these iron-propargyl complexes.

Propargyl complexes of ruthenium

Abstract The first ruthenium-propargyl complexes CpL 2 RuCH 2 C=CPh (LCO ( 1 ) and PPh 3 ( 2 )) were synthesized by reaction of [Cp(CO) 2 Ru] − with PhCCCH 2 Cl or PhCCCH 2 OS(O) 2 C 6 H 4 Me- p and of Cp(PPh 3 ) 2 RuCl with PhC CCH 2 MgCl, respectively. In contrast, treatment of [Cp(CO) 2 Ru] − with HCCCH 2 Cl affords the ruthenium-η 1 -allenyl complex Cp(CO) 2 RuCHCCH 2 ( 3 ). Complex 1 is protonated by HBF 4 ·OEt 2 to ( syn -Cp(CO) 2 Ru(η 2 CH CCHPh)]BF 4 ( 4a ), which isomerizes within 2 h in acetone solution at room temperature to [ anti -Cp(CO) 2 Ru(η 2 -CH 2 CCHPh)]BF 4 ( 4b ). Compound 4b reacts with Pt(PPh 3 ) 2 (C 2 H 4 ) to give the ruthenium-substituted platinum (II)-η 3 allyl complex [(η-CH 2 C(Ru(CO) 2 Cp)CHPh)Pt(PPh 3 ) 2 ]BF 4 as the anti isomer quantitatively. Compound 1 undergoes facile [3 + 2] cycloaddition reactions with tetracyanoethylene (TCNE) and p -toluenesulfonyl isocyanate (TSI); the latter reaction in CH 2 Cl 2 solution at 25°C proceeds slightly more rapidly (1.3 times) than the corresponding reaction of Cp(CO) 2 FeCH 2 CCPh. With Co2(CO) 8 , 1 yields the trinuclear (CO) 3 Co(μ-η 2 -PhCCCH 2 Ru(CO) 2 Cp)Co(CO) 3 , which undergoes very slow cleavage of the RuCH 2 bond with CF 3 CO 2 H, and replacement of CO (at Co) with PPh 3 . The foregoing reactions are compared and contrasted with the corresponding reactions of Cp(CO) 2 FeCH 2 CCPh. Where a comparison has been made, 2 was found to react faster than 1; however, its chemistry tends to be complicated by the lower stability of products and a facile PPh 3 -Co ligand exchange. With TSI and CO 2 (CO) 8 , the products are analogous to those of 1 but with Fe 2 (CO) 9 Cp(CO)PPh 3 )RuCH 2 CCPh and Fe(CO) 4 PPh 3 are obtained instead of heteronuclear metal complexes.

A kinetic study of the cleavage of the ironcarbon σ bond in η5-C5H5Fe(CO)2R by halogenated acetic acids

Abstract The rates of the reaction of η5-C5H5Fe(CO)2R (R = alkyl and aryl) with CF3CO2H to give η5-C5H5Fe(CO)2OC(O)CF3 and RH wre investigated in organic solvents, mostly at 25°C, by infrared spectroscopic, manometric and volumetric techniques. When R = alkyl, the cleavage in CH2Cl2 is first order in η5-C5H5Fe(CO)2R and first order in the CF3CO2H monomer at acid concentrations ⪆0.1M, but first order in η5-C5H5Fe(CO)2R and second order in the CF3CO2H monemer at lower acid concentrations. The dependence of the second-order rate constant on R follows the order C5H5 > CH5Si(CH3)3 (>110) > CH3 (32) > n-C4H9 (15) > C2H5 (11) > CH2C(CH3)3 (6.2) > CH2CH2C6H5 (5.3) > CH(CH3)C6H5 (∼1.2) ⪆ CH2C6H5 (1.0) > CH(CH3)2. The isotope effect, k2/kD, for the cleavage of η5-C5H5Fe(CO)2CH3 by CF3CO2H and CF3CO2D is 4.7. Solvent influence on the rate of the FeCH3 bond scission in CH2Cl2, CH2ClCH2Cl and C6H6 is very small. A mechanism is proposed which involves the formation of an Fe-H-OC(O)CF3 hydrogen-bridged 1 1 adduct of the reactants in a reversible step. This adduct then affords [η5-C5H5Fe(CO)2(R)H][CF3CO2H·O2CCF3] with the assistance of a second molecule of CF3CO2H. Reductive elimination of RH and coordination to iron of CF3CO2− complecte the reaction. The corresponding cleavage of a given FeR bond by CHCl2CO2H is substantially slower than that by CF3CO2H; for the aryl complexes it follows the order R = p-C6H4CH3 > p-C6H4F > C6H5 > p-C6H4Cl, with p ∼ −5.4.

The stereospecificity at the iron center of the decarbonylation of an ironacetyl complex

Abstract The dinuclear complex [( h 5 -1-CH 3 -3-C 6 H 5 C 5 H 3 )Fe(CO) 2 ] 2 was synthesized by reaction of Fe 2 (CO)9 with 1-methyl-3-phenylcyclopentadiene; it was converted to ( h 5 -1-CH 3 -3-C 6 H 5 C 5 H 3 )Fe(CO) 2 CH 3 by reduction with sodium amalgam and addition of CH 3 l, and thence to ( h 5 -1-CH 3 -3-C 6 H 5 C 5 H 3 )Fe(CO)[P(C 6 H 5 ) 3 ] (COCH 3 ) (I) by reaction with P(C 6 H 5 ) 3 . The acetyl I was separated into two diastereomerically related pairs of enantiomers. Ia and Ib, by a combination of column chromatography on alumina and crystallization from benzene/pentane. The photochemical decarbonylation of Ia and Ib in benzene or THF solution was examined by 1 H NMR spectroscopy. This reaction proceeds with high stereospecificity (>84% retention or inversion) at the iron center to yield ( h 5 -1-CH 3 -3-C 6 H 8 C 5 H 3 )Fe(CO)[P(C 6 H 5 ) 3 ]CH 3 (II), enriched in the diastereomerically related pairs of enantiomers, IIa and IIb, respectively. Since IIa and IIb epimerize under the photolytic conditions of decarbonylation, the actual stereospecificity of the conversion of I to II is higher than 84%, and likely 100%. This is supported by the data from kinetic studies of the decarbonylation of I and the epimerization of II, carried out under identical photolytic conditions. The implications of the foregoing results to the mechanism of the decarbonylation are considered. Also described herein is the synthesis of other complexes with two asymmetric centers of the general formula ( h 5 -cyclopentadienyl)Fe(CO)(L)(COR) and ( h 5 -cyclopentadienyl)Fe(CO)(L)R that contain either an unsymmetrically substituted h 5 -cyclopentadienyl ring or a chiral tertiary phosphine.

Sulfur dioxide insertion IX. Sulfinato complexes of divalent mercury

Interaction of HgR2 (R = C6H5, C2H5, and CH2C6H5) with liquid sulfur dioxide at -40° to -10° affords virtually quantitative yields of the corresponding monosulfinates, RSO2HgR. At low temperatures (ca. -70°), (C2H5Hg)2SO2 usually becomes a by-product of the reaction between Hg(C2H5)2 and SO2. The new compounds have been characterized by chemical analyses, molecular weight measurements, and IR and NMR spectroscopy. The phenylsulfinate, C6H5SO2HgC6H5, has been isolated in two isomeric forms which are S- and O-bonded. The latter arises from the former on crystallization; it also appears to be the prevalent species on solution, where it is monomeric. The ethylsulfinate, C2H5SO2HgC2H5, is S-bonded in the solid but adopts a monomeric, O-bonded structure in solution; the benzylsulfinate, C6H5CH2SO2HgCH2C6H5, has been assigned a monomeric, O-bonded structure both in the solid and in solution.

Photochemistry of methyl- and n1-benzyl-n5-cyclopentadienyltricarbonyltungstein(II)

Abstract Irradiation of solutions of n 5 -C 5 H 5 W(CO) 3 R (R  CH 3 n 1-CH 2 C 6 H 5 ) in cyclohexane at ca. 310490 nm leads to the formation of [n 5 -C 5 H 5 W(CO) 3 ] 2 and methane and of n 5 -C 5 H 5 W 5 (CO) 2 ( n 3 -CH 2 C 6 H 5 ) and some [ n 5 -C 5 H 5 W(CO) 3 ] 2 , respectively. When the irradiation is carried out in the presence of excess P(C 6 H 5 ) 3 , the photoproducts are n 5 -C 5 H 5 W(CO) 2 [P(C 6 H 5 ) 3 ]CH 3 (R  CH 3 ) and n 5 -C 5 H 5 W(CO) 2 (n 3 -CH 2 C 6 H 5 ) and trace [ n 5 -C 5 H 5 W(CO) 3 ] 2 (R  n 1 -CH 2 C 6 H 5 ). Photolysis of the n 5 -C 5 H 5 W(CO) 3 R in the presence of benzyl chloride affords n 5 -C 5 H 5 W(CO) 3 Cl (R  CH 3 ) and both n 5 -C 5 H 5 W(CO) 2 ( n 3 -CH 2 C 2 H 5 ) and n 5 -C 5 H 5 W(CO) 3 Cl (R  n 1 -CH 2 C 6 H 5 ), the relative amounts of the latter products depending on the quantity of added C 6 H 5 CH 2 Cl. Irradiation of n 5 -C 5 H 5 W(CO) 3 -CH 3 in the presence of both P(C 6 h 5 ) 3 and C 6 H 5 CH 2 Cl affords n 5 -C 5 H 5 W(CO) 2 -[P(C 6 H 5 ) 3 ]CH 3 , but no n 5 -C 5 H 5 W(CO) 3 Cl. It is proposed that the primary photo-reaction in these transformations is dissociation of a CO group from n 5 -C 5 H 5 W-(CO) 3 R to generate n 5 -C 5 H 5 W(CO) 2 R, which can either combine with L to form a stable 18 electron complex, n 5 -C 5 H 5 W(CO) 2 (L)R (L  CO, P(C 5 H 5 ) 3 ; LR  n 3 -CH 2 C 6 H 5 ), or lose the group R in a competing, apparently slower step. This proposal receives support from the observation that, light intensifies being equal, n 5 -C 5 H 5 W(CO) 3 CH 3 undergoes a considerably faster photoconversion to [ n 5 -C 5 H 5 W(CO) 3 ] 2 under argon than under carbon monoxide.