Terminal CO Research Articles

Unusually labile organoplatinum complexes: a mechanistic study of insertion–deinsertion into platinum–alkyl complexes of pyridine-2-carboxylic acid

Platinum–alkyl complexes of the general formula [PtR(pyca)L][R = Me, Hpyca = pyridine-2-carboxylic acid, L = PPh3, P(CH2Ph)3, P(C6H11)3, pyridine or 4-methylpyridine; R = Et, L = PPh3 or P(CH2Ph)3] and the complex [PtMe(hoqu)(PPh3)](Hhoqu = 8-hydroxyquinoline) have been prepared and their carbonylation activity studied. The complexes show a large variation in carbonylation behaviour, which is markedly dependent on the ligands attached to the platinum centre. The donor capacity of L and the rigidity of the chelating ligand are major factors. For complexes containing pyca as the chelating ligand; where R = Me or Et and L = PPh3, acyl complexes are readily prepared; where R = Et and L = P(CH2Ph)3, a mixture of two products is formed, the expected acyl complex [Pt(COEt)(pyca){P(CH2Ph)2}] and a compound with a terminal CO ligand in which the pyca ligand is monodentate [Pt(CO)(COEt)(pyca){P(CH2Ph)3}]; where L = P(C6H11), pyridine or 4-methylpyridine, no carbonylation occurs. With the complex containing the rigid hoqu ligand no carbonylation occurs. The complexes [Pt(COMe)(pyca)-(PPh3)] and [PtEt(pyca)(PPh3)] are unusually labile, eliminating CO or ethylene when warmed, giving [PtMe(pyca)(PPh3)] or platinum–hydride complexes respectively. The behaviour of these complexes and the carbonylation behaviour of the platinum–alkyl complexes has been studied in detail and a mechanism for the insertion–deinsertion reactions is proposed.

Crystal structure and intramolecular dynamics of [Ir 3Rh(CO) 8(η 4-cycloocta-1,5-diene) 2

The redox condensation of [Ir(CO) 4] −, [Ir(COD)(THF) 2] + and [Rh(COD)(THF) 2] − (COD = cycloocta-1, 5-diene) yields [Ir 3Rh-(CO) 8(η 4-COD) 2] ( I). X-ray diffraction shows that I contains three edge- bridging CO's defining a basal Ir 2Rh face of the metal tetrahedron, and two COD chelating the Rh atom and one basal Ir atom, respectively. In solution this structure is static on the NMR time scale up to ca. 220 Y, Above that temperature CO scrambling occurs due to the rotation of three terminal CO's about a local C 3 axis on the apical Ir atom. The reaction of I with CO (1 arm) in THF affords the first synthetic route to pure [Ir 3Rh(CO) 12].

Synthesis, Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2

AbstractThe synthesis of [Ir2Rh2(CO)12] (1) by the literature method gives a mixture 1/[IrRh3(CO)12] which cannot be separated using chromatography. The reaction of [Ir(CO)4]− with 1 mol‐equiv. of [Rh(CO)2(THF)2]+ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir2Rh2(CO)5(μ2‐CO)3(norbornadiene)2] which were analysed using X‐ray diffraction. The ground‐state geometry of 1 in solution has three edge‐bridging CO's on the basal IrRh2 face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D‐ and VT‐13C‐NMR. Substitution of CO by X− in 1 takes place at a Rh‐atom giving [Ir2Rh2(CO)8(μ2‐CO)3X]− (X = Br, I). Substitution by bidentate ligands gives [Ir2Rh2(CO)7(μ2‐CO)3(η4‐L)] (L = norbornadiene, cycloocta‐1,5‐diene) where the ligand L is chelating a Rh‐atom of the basal IrRh2 face. Carbonyl substitution by tridentate ligands gives [Ir2Rh2(CO)6(μ2‐CO)3(μ3‐L)] (L = 1,3,5‐trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C3 axis on the apical Ir‐atom.

FT-IRAS study of CO adsorption, desorption and displacement reaction by NO on Ni(100)

The CO adsorption, desorption and displacement by NO on Ni(100) have been studied by Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). The adsorption and desorption processes are studied by time-resolved IRAS. The reversible site-conversion of adsorbed CO between the terminal site and the bridged site at low coverage are studied between 80 K and 220 K, where the binding energy difference is determined to be 11 meV. The displacement reaction of CO by NO at room temperature occurs predominantly from the terminal CO and all the adsorbed CO species are removed finally. The main driving force of the displacement is attributed to the dissociative adsorption of NO on Ni(100) at room temperature.

In situ infrared investigation of alkylation reaction of dianionic triruthenium ketenylidene cluster on magnesium oxide with methyl iodide

AbstractThe reation between [Ru3(CO)9(CCO)]2− supported on magnesium oxide and alkylating agent CH3I was investigated in an attempt to understand its reactivity and mechanism by using FT‐IR technique. The IR spectra show that [Ru3(CO)9(CCO)]2−/MgO reacts with CH3I to produce [Ru3(CO)9CC(O)CH3]−/MgO, which exhibits bands at 2960, 2022, 1988, 1638, 1460 and 1350 cm−1. The absorption at 2960, 1460 and 1350 cm−1 are attributed to ‐CH3 group, while bands at 2022, 1988 and 1952 cm−1 are assigned to the terminal CO groups attached to ruthenium. The band at 1638 cm−1 was assigned to acyl carbonyl. Isotopes labeled compounds CD3I, 13CO and [Ru3(CO)9(*C*CO)]2− were used in investigation. The results demonstrate that β‐carbon of CCO ligand is attacked by CH+3 species and produces [Ru3(CO)9CC(O)CH3]−/MgO.

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge‐bridging bidentate ligands

AbstractThe fluxionality of [Ir4(CO)8(μ2‐CO)3L] (L = Br−, I−, SCN−, NO2−, P(4‐ClC6H4)3, PPh3, P(4‐MeOC6H4)3, P(4‐Me2NC6H4)3), as studied by 2D‐13C‐NMR in solution, is due to two successive scrambling processes: the merry‐go‐round of six basal CO's and CO bridging to alternative faces of the Ir4 tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir4(CO)7(μ2‐CO)3(PMePh2)2] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir4(CO)10(μ2‐LL)] with one edge‐bridging ligand have a ground‐state geometry with three edge‐bridging CO's (LL = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (LL = CH3SCH2SCH3). In all cases, the fluxional process of lowest activation energy in the merry‐go‐round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir‐atoms residing on the mirror plane of the unbridged intermediate.

Natural abundance 17O NMR spectra of carbonyl metal clusters of the iron triad

17O NMR spectra (in natural abundance) have been recorded, at room temperature, for a variety of polynuclear iron, ruthenium and osmium carbonyl clusters. Rather sharp linewidths have been observed for stereochemically rigid species, whereas linewidths as large as about 200 Hz have been obtained for fluxional molecules. Even though the observed chemical shift range for terminal CO groups is not very large (about 50 ppm), taking into account linewidths, metal triad and substituent effects have been observed to different extents.

The crystal structure of Co 6C(CO) 12E2 (E = Se) and its relevance to the vibrational spectra of the species E = S, Se

Co 6C(CO) 12Se 2 crystallizes in the monoclinic system, space group Cc with a = 16.365(4) Å, b = 9.429(2) Å, c = 17.479(5) Å, β = 122.75(2)°, Z = 4 and (Mo — K a ) = 0.71070 Å. The final reliability indices are R = 0.051 and R W = 0.048 for 2081 observed reflections having F > 4.0σ( F). The molecule consists of a Co 6 trigonal prism with the triangular faces capped by selenium atoms. Each cobalt is bonded to two terminal CO groups. A carbon atom is embedded at the centre of the Co 6 prism. The Raman spectra of polycrystalline samples of this compound and of the sulphur analogue have been recorded. These, together with the corresponding infrared data, can only be understood in terms of a dominant intermolecular coupling on the ν(Co—E) modes (E = S, Se). The origin of this coupling is the close contact between neighbouring clusters in one distinct direction which gives rise to a chain of molecules in the crystal. The significant effect of these oriented close contacts on the vibrational modes is demonstrated.

Site conversion of CO on Ni(100): binding-energy difference and role of low-energy hindered vibrations

The site conversion of adsorbed CO between the terminal site and the bridged site on Ni(100) was studied by means of infrared reflection absorption spectroscopy. The temperature dependence of the relative occupation for two sites was measured from 80 to 220 K in detail, where the binding-energy difference was determined to be 11 meV. Predominant occupation of the terminal site at higher temperatures is due to the thermal excitation of the low-energy degenerate hindered translational mode of the terminal CO.

Electrostatic-field effects on adsorbate bonding and structure at metal surfaces: parallels between electrochemical and vacuum systems

The observed effects of varying the surface potential, and hence the accompanying electrostatic fields, upon adsorbate bonding at ordered monocrystalline metals in electrochemical environments are summarized and discussed in comparison with field effects at related metal-vacuum interfaces for the specific case of carbon monoxide. The dependencies of the C-O stretching frequency, ν CO, upon the electrochemical surface potential, E (and interfacial field, E ), as evaluated for CO adlayers at a fixed coverage, θ; CO, and surface binding site are summarized as a function of θ CO, the metal substrate, and the double-layer ionic environment, in order to illustrate the virtues of electrochemical systems for exploring such interfacial field effects. The increasing preference for multifold versus terminal CO binding commonly observed towards lower potentials (and at larger negative fields) is also noted. These findings are compared with related field-induced effects observed for metal-CO adlayers in vacuum and also for chargeable metal-carbonyl clusters in solution. Variations in field for the former systems are induced by postdosing dipolar or ionizable coadsorbates, or by applying an external electrostatic field. Some physical differences as well as similarities in the electrostatic fields present for such systems are noted. The ν CO- E dependencies observed for the different systems are compared briefly with the predictions of theoretical models which account for potential-dependent surface-adsorbate bonding and interfacial field-induced Stark effects.

Crystal structure of Co4(CO)10S2 and Co4(CO)10Se2; v(CO) vibrations of a model cluster molecule: Co4(CO)10S2

The crystal structure of Co4(CO)10S2 has been redetermined and that of Co4(CO)10Se2 obtained by X-ray analysis. The compounds are monoclinic and isomorphous, space groupP21/n,Z=2, with (S compound)a=10.42(2)A,b=6.794(1)A,c=12.421(2)A,β=97.27(1) and (Se compound)a=10.110(2)A,b=6.747(2)A,c=12.592(4)A,β=96.37(2); finalR(S)=0.029,R w =0.032 for 1414 reflections and finalR (Se)=0.052,R w =0.054 for 1264 reflections. The molecules, which lie on a crystallographic center of symmetry, consist of a rectangle with Co atoms at the corners, each face of the rectangle being capped by a chalcogen atom. Each Co atom is bonded to two terminal CO groups; there are two bridging CO groups, one on each member of a pair of opposite sides of the rectangle. The vibrational spectra of the sulfur compound are considered in detail. A study of the crystal structure, and recognition of an approximate spectroscopic space group, are shown to be essential for an understanding of thev(CO) infrared spectrum of polycrystalline Co4(CO)10S2. In this molecule, intramolecular vibrational coupling in the crystal leads to extensive modifications of the infrared-activev(CO) molecular coordinates.

Application of the hydro(solvento)thermal technique to the synthesis of metal carbonyl chalcogenide clusters. 2. Synthesis and x-ray structures of [[Fe4Te4(CO)10]2(Te2)]2- and [[Fe2Se(CO)6]2(Se2)]2-

The hydrothermal reaction of Fe(CO)[sub 5] with Na[sub 2]Te[sub 2] in the presence of Ph[sub 4]PCl at 110[degrees]C forms (Ph[sub 4]P)[sub 2][[l brace]Fe[sub 4]Te[sub 4](CO)[sub 10][r brace][sub 2](Te[sub 2])] (I) while the reaction of Fe(CO)[sub 5] with Na[sub 2]Se[sub 2] in superheated methanol at 80[degrees]C results in (Ph[sub 4]P)[sub 2][[l brace]Fe[sub 2]Se(CO)[sub 6][r brace][sub 2](Se[sub 2])] (II). The structures of (I) and (II) were determined by X-ray single-crystal analysis. (I) crystallizes in the space group P[bar 1], and (II) in the space group P2[sub 1]/n. The [[l brace]Fe[sub 4]Te[sub 4](CO)[sub 10][r brace][sub 2](Te[sub 2])][sup 2[minus]] anion in (I) forms a ditelluride, Te[sub 2][sup 2[minus]], bridged double cubane-like structure with eight iron atoms in two Fe[sub 4]Te[sub 4] cubes being octahedrally-coordinated by briding tellurium ligands and terminal CO groups. The [[l brace]Fe[sub 2]Se(CO)[sub 6][r brace][sub 2](Se[sub 2])][sup 2[minus]] molecule in (II) adopts a double butterfly' conformation caused by an intramolecular Se-Se linkage between two Fe[sub 2]Se[sub 2](CO)[sub 6] units. All iron atoms in this structure have a distorted octahedral geometry achieved by selenium ligands, CO groups, and a Fe-Fe single bond. The average Fe-Te bond distance is 2.619(4) [Angstrom], and Fe-Se = 2.386(17) [Angstrom]. 30 refs., 4 figs., 5 tabs.

Umsetzung von alkinylphosphanen mit hauptgruppenelement-verbr:uckten eisencarbonylclustern

The tetrahedral clusters Fe 3(CO) 10(μ 3-PR) ( 1) react on thermal as well as photochemical activation with Ph 2PCCPh to give Fe 3(CO) 8(μ 3-PR)[μ 3-η 4-Ph 2PCCph(CO)] ( 3). In 3 an edge-opened iron triangle bears a μ 3-PR group on one side and the alkynylphosphane on the other side as bridging moieties. One of the terminal CO groups present in 1 in addition to being coordinated to the appropriate iron atom, is bonded to the phenylsubstituted carbon atom of the alkynylphosphane. Irradiation of the square-pyramidal cluster Fe 3(CO) 9(μ 3-P tBu)(μ 3-Se) ( 2) in the presence of Ph 2PCCPh leads to the compounds Fe 3(CO) 7(Ph 2PCCPh) 2(μ 3-P tBu)(μ 3-Se) ( 4) and Fe 3(CO) 6(Ph 2PCCPh) 3(μ 3-P tBu)(μ 3-Se) ( 5). In these clusters the square-pyramidal framework of 2 is preserved. In each case the alkynylphosphane ligands are coordinated via phosphorus only. In 4 one of these ligands is bonded to each of the two equatorial iron centres; in 5 each of the three iron atoms bears an alkynylphosphane ligand. The results are supported by conventional spectroscopic and analytical data as well as by single-crystal analyses.

Preparation of organic solutions or solid films of small particles of ruthenium, palladium, and platinum from organometallic precursors in the presence of cellulose derivatives

Reaction of Ru(cod)(cot) with hydrogen in the presence of nitrocellulose (NC) or cellulose acetate (CA) at 20[degree]C yields colloidal ruthenium solutions containing particles of 10, 15, and 20 [angstrom], respectively, and showing a low dispersity for concentrations in Ru of 2, 5, and 10 wt% (NC) or particles of average size 15, 20, and 25 [angstrom] for concentrations in Ru of 2, 5, and 10 wt% (CA). No change in particle size is observed upon reaction with CO in NC whereas agglomeration occurs in CA. The infrared spectra of CO adsorbed on Ru colloids have been recorded. Whatever the stabilizing polymer, two bands were observed. A band at 2030 cm[sup [minus]1] has been assigned to the stretching vibration of CO linearly adsorbed on the Ru surface. A low-frequency band at 1965 cm[sup [minus]1] has been assigned to bridging CO. The relative intensities of these two bands were found to vary with particle size. Reaction of M(dba)[sub 2] (M = Pd, Pt; dba = dibenzylidene acetone) under CO in the presence of NC or AC leads to colloidal solutions containing small metal particles (respectively 35 [angstrom] for Pd in NC or CA, 12 [angstrom] for Pt in NC, 15 [angstrom] formore » Pt in CA independent of metal/polymer concentration). The presence of coordinated CO was observed in all cases. At maximum coverage, palladium colloids showed 3-fold and 2-fold bridging CO respectively at 1950 and 1890 cm[sup [minus]1]; platinum colloids showed both bridging and terminal CO at 1880 and 2050 cm[sup [minus]1]. 35 refs., 7 figs.« less

Stereochemistry of the compounds [Fe 3(CO) 9XY]. Crystal and molecular structures of the mixed triiron carbonyl compounds [Fe 3(CO) 9XY] (X, Y = S, Se, or Te)

X-ray analyses of [Fe 3(CO) 9SSe], [Fe 3(CO) 9STe] and of [Fe 3(CO) 9SeTe] was performed. The three compounds are isomorphous and belong to the trielinic space group P 1 with a = 6.835(1), 6.996(1), 6.964(1) Å, b = 9.186(2), 9.367(1), 9.360(2) Å, c = 13.121(3), 13.058(2), 13.189(2) Å, α = 93.79(3), 93.23(1), 94.09(2)°, β = 94.21(3), 94.03(1), 94.54(2)° γ = 110.89(3), 111.14(1), 110.67(2)° for the SSe, STe and SeTe complexes, respectively. The structures were refined anisotropically to R = 0.026, 0.042, 0.030 for 3127 3465, 2564 observed reflections for the SSe, STe and SeTe complexes, respectively. They belong to the well known series of [Fe 3(CO) 9XY] complexes formed by an open triangle of iron atoms each linked to three terminal CO groups, with two faces capped by a chalcogen atom. The bond distances and angles of these mixed complexes are well within the ranges imposed due to the different dimensions of the chalcogen atoms. Intermolecular contacts occur when at least one chalcogen atom is tellurium. Examining some relevant geometrical features of the complexes with X,Y = S, Se, Te, NR, PR, AsR… a regular trend of the Fe-Fe distances is found, depending on the dimensions of the capping atoms; an asymmetry of the Fe-Fe distances is attributed to steric factors.

Synthesis, structure, and chemistry of heterobimetallic phosphidobridged complexes CpFe(CO) 2(μ-PPh 2) M(CO) 5 (M  Cr, Mo, W)

A series of new non-metal-metal bonded heterobimetailic phosphido-bridged complexes CpFe(CO) 2(μ-PPh 2)M(CO) 5 (M  Cr, Mo, W) was synthesized by reaction of LiPPh 2M(CO) 5 (M  Cr, Mo, W) with CpFe(CO) 2I. Results from single-crystal X-ray diffraction studies of the FeMo and FeCr complexes indicated that Fe was ligated by one C 5H 5 and two terminal CO. Five CO groups were coordinated to M (M  Cr, Mo). The long distances between Fe and M in phosphido-bridged complexes indicated no metal-metal bond to exist. Removal by photolysis of one CO from the FeW complex produced Cp Fe(CO)(μ-CO)(μ-PPn 2)W (CO) 4. The corresponding FeCr and FeMo analogues were found to be inert to UV radiation.

Synthesis of [Co2(µ-PPh2C3H4)(µ-PPh2)(CO)4]; its reactions with P(OMe)3and with alkynes

The bis(phosphido)-bridged complex [Co2(µ-PPh2)2(CO)6]1 undergoes an insertion reaction of allene into one of the phosphido bridges, to give the new ligand-bridged dinuclear cobalt complex [Co2(µ-PPh2C3H4)(µ-PPh2(CO)4]2 in high yield. Complex 2 reacts with P(OMe)3 to give the monosubstituted derivative [Co2(µ-PPh2C3H4)(µ-PPh2)(CO)3{P(OMe)3}]3 in which substitution has occurred at the allyl-co-ordinated cobalt atom. Complex 2 also reacts with alkynes, RCCH (RCH2OH, Me or H), which insert into the remaining phosphido bridge along with a molecule of CO to give [CO2(µ-PPh2C3H4){µ-PPh2C(O)CHCR}(CO)3](R = CH2OH 4a, Me 4b or H 4c). In the case of MeCCH which gives 4b, a second isomer, [Co2(µ-PPh2C3H4){µ-PPh2C(O)CMeCH}(CO)3]5, which differs in the mode of insertion of the alkyne, is also obtained. The isomeric complexes [Co2{µ-PPh2C(O)CHCR}(µ-PPh2)(CO)4](R = CH2OH 6a or Me 6b) and [Co2{µ-PPh2C(O)CRCH}(µ-PPh2)(CO)4](R CH2OH 7a or Me 7b), which may be regarded respectively as analogues of 4 and 5 but with a phosphido bridge and an additional terminal CO group in place of the µ-PPh2C3H4 ligand, have been prepared from [Co2(µ-RCCH)(CO)6](R CH2OH or Me) and P2Ph4. The complexes [Co2{µ-PPh2CHCRC(O)}(µ-PPh2)(CO)4](R CH2OH 8a or Me 8b), which are also isomers of complexes 6a, 7a and 6b, 7b respectively, have also been obtained in these latter reactions. The complexes 8 contain a bridging ligand which differs from that present in 6 and 7 in that the ordering of the PPh2, alkene and CO components of the bridging ligand is not the same. The crystal structures of the complexes 3 and 4c have been determined by X-ray diffraction studies.

Crystal and molecular structure of bis(μ 3-tellurido)-decacarbonyltriiron, [Fe 3(CO) 10Te 2

The tellurium complex [Fe 3(CO) 9Te 2] reacts with CO to give [Fe 3(CO) 10Te 2]. The reaction occurs via attack of CO on a peripheral iron atom of the open triangle of [Fe 3(CO) 9Te 2] with consequent rupture of an iron—iron bond. The complex lies on a crystallographic two-fold axis and contains an iron—iron bond between two Fe atoms each linked to three terminal carbonyl groups: a third Fe atom, linked to four terminal CO groups, is connected to the Fe 2 unit by two bridging Te atoms.

Thiocarbonyl complexes of iron VIII. Reaction of Fe(CO) 4CS with the halogens Cl 2, Br 2 and I 2

The halogens Br 2 and I 2 convert the thiocarbonyl complex Fe(CO) 4CS ( 1) by oxidative addition into the corresponding complexes Fe(CO) 3(CS)X 2 ( 3:XBr, I). Treatment of 3 at −80 °C with two equivalents of PPh 3 yields the thiocarbonyl complexes Fe(CO)(CS)(PPh 3) 2X 2 ( 4). The action of Cl 2 on 1 produces an unidentified black insoluble material containing terminal CO and CS groups. The compounds have been characterized by elemental analysis, IR, 31P NMR and mass spectroscopy. Based on the spectroscopic results, a cis arrangement of the halogen atoms is discussed.

Synthesis and characterization of Cp2Zr(CH{Me}{6-ethylpyrid-2-yl})(CO)+, a d0 metal alkyl carbonyl complex. Coordination chemistry of the four-membered azazirconacycle Cp2Zr(.eta.2-C,N-CH{Me}{6-ethylpyrid-2-yl})+

The cationic complex Cp{sub 2}Zr(CH{sub 3})(THF){sup +} (1, as the BPh{sub 4}{sup {minus}} salt) reacts with 2,6-diethylpyridine to afford the chelated secondary zirconocene-alkyl complex Cp{sub 2}Zr({eta}{sup 2}-C,N-CH(Me)(6-ethylpyrid-2-yl)){sup +} (2). Treatment of complex 2 with CO, CH{sub 3}CN, {sup t}BuCN, and (PhCH{sub 2})(Et){sub 3}N{sup +}Cl{sup {minus}} affords Cp{sub 2}Zr(CH(Me)(6-ethylpyrid-2-yl))(CO){sup +} (3), Cp{sub 2}Zr(CH(Me)(6-ethylpyrid-2-yl))(CH{sub 3}CN){sup +} (4), Cp{sub 2}Zr(CH(Me)(6-ethylpyrid-2-yl))({sup 5}BuCN){sup +} (5), and Cp{sub 2}Zr(CH(Me)(6-ethylpyrid-2-yl))(Cl) (6), respectively. The thermally sensitive d{sup 0} carbonyl complex 3 is a rare example of a d{sup 0} M(alkyl)-CO adduct and is unambiguously characterized in solution by low-temperature NMR and IR spectroscopy, {sup 13}C-labeling and hydrolysis experiments, and decomposition studies. IR and NMR data establish that 3 contains a terminal CO ligand. An X-ray structure analysis of 6 established that the CH(Me)(6-ethylpyrid-2-yl) ligand adopts a chelated structure; the similarity of the spectroscopic data for 3-6 implies that 3-5 have similar chelated structures. At room temperature, 3 in CD{sub 2}Cl{sub 2} rapidly decomposes to afford a complex mixture of products. {sup 1}H NMR monitoring of the decomposition of 3 reveals formation of a transient cationic zirconocene-acyl intermediate 9, which undergoes 1,2-H shift to afford a mixture of isomeric/oligomeric zirconocene-enolates. Treatment of this mixture with (PhCH{sub 2})(Et){sub 3}N{sup +}Cl{supmore » {minus}} affords Cp{sub 2}Zr(OCH=C(Me)(6-ethylpyrid-2-yl)) Cl (10) as a mixture of E/Z isomers, establishing the presence of zirconocene-enolate species. Hydrolysis of the decomposition products of 3 affords a mixture of thermally sensitive tautomers, enol 11/aldehyde 11{prime}, which are characterized by NMR, FTIR, and mass spectroscopy. 39 refs., 6 figs., 3 tabs.« less