Carbonyltungsten(0) complexes of acryloylferrocene: Synthesis and characterization

Photolysis of hexacarbonyltungsten(0) in the presence of acryloylferrocene in n-hexane solution at 10 °C yields pentacarbonyl(η²-acryloylferrocene)tungsten(0) (1) as the only photo-substitution product, different from the general reaction pattern observed for the Group 6 metal carbonyls with other olefins. W(CO)₅(η²-acryloylferrocene) (1) decomposes in solution to the parent hexacarbonyltungsten(0) and free acryloylferrocene. Trimethylphosphite was introduced as ligand into the molecule to increase the stability. The photolysis of pentacarbonyl(trimethylphosphite)tungsten(0) in the presence of acryloylferrocene in n-hexane solution at 10 °C yields only cis-W(CO)₄[P(OCH₃)₃](η²-acryloylferrocene) (2) as the monosubstitution product. Both η²-acryloylferrocene complexes (1 and 2) could be isolated and characterized by MS, IR and NMR spectroscopy. The trimethylphosphite complex (2) is found to be even less stable than W(CO)₅(η²-acryloylferrocene) (1).     

Reductive elimination reaction of rhenium complexes trans-(η-C5Me5)Re(CO)2(chloroaryl)Cl

Thermal reaction of the chloroaryl-chloride complexes trans-(η⁵-C₅Me₅)Re(CO)₂(Ar^Cl)Cl (Ar^Cl = 3-ClC₆H₄, 3-ClC₆H₃(4-Me) and 3,5-Cl₂C₆H₃) in acetonitrile did not interconvert to the cis isomer, instead the complex ReCl(CO)₂(NCMe)₃ and the corresponding 5-Ar^Cl-1,2,3,4,5-pentamethylcyclopentadiene were formed. Similar reductive elimination products were obtained when the starting rhenium complexes were reacted with trimethylphosphite in toluene.     

Syntheses and crystal structures of straight or zigzag one-dimensional coordination polymers based on Cu(II) square pyramidal or Cu(I) tetrahedral coordination environments

Two coordination polymers containing copper ions, [Cu(SO₄)(pyz)(H₂O)]_n (1) and [Cu₂(SO₄)(pyz)₂(H₂O)₂]_n (2) (pyz = pyrazine), have been synthesized and characterized by single-crystal X-ray analyses. Compound 1 was synthesized by the reaction of Cu(SO₄) · 5H₂O with pyz (ratio = 1:2) in H₂O at room temperature. The structure of 1 consists of linear chains of [Cu(pyz)(H₂O)]²⁺, with coordinated sulfate ions bridging the chains. Compound 2 was obtained as dark red blocks from the reaction of Cu(SO₄) · 5H₂O and pyz (ratio = 1:2) in H₂O, after heating to 180 °C in a Teflon autoclave for 48 h. The structure of 2 consists of zigzag chains of [Cu(pyz)(H₂O)]⁺ with sulfate ions. Only the difference in the synthesis temperature, room temperature or 180 °C, determines whether Cu(II) or Cu(I) coordination polymers are formed, with the reduction of Cu(II) to Cu(I) being explained by the Gillard mechanism.     

Syntheses, crystal structures and DFT studies of [Me3EM(CO)5] (E = Sb, Bi; M = Cr, W), cis-[(Me3Sb)2Mo(CO)4], and [Bu3BiFe(CO)4]

Syntheses of [Me₃SbM(CO)₅] [M = Cr (1), W (2)], [Me₃BiM(CO)₅] [M = Cr (3), W (4)], cis-[(Me₃Sb)₂Mo(CO)₄] (5), [^tBu₃BiFe(CO)₄] (6), crystal structures of 1-6 and DFT studies of 1-4 are reported.     

Octahedral metal carbonyls : XL. A reinvestigation of the kinetics and mechanism of ligand exchange in (2,2,8,8-tetramethyl-3,7-dithianonane)- tetracarbonyltungsten(0)

A reinvestigation of the kinetics and mechanism of ligand-exchange reactions of (2,2,8,8-tetramethyl-3,7-dithianonane)tetracarbonyltungsten(0) ((DTN)W(CO)₄) with alkyl and aryl phosphites (L) to afford trans- and cis-L₂W(CO)₄ products supports a mechanism involving initial ring-opening, and subsequent competition between ring-reclosure and attack at the “ring-opened” five-coordinate, probably fluxional, intermediate, by L. A competing path, involving ring-reclosure in cis-(η¹-DTN)W(CO)₄(L) species with expulsion of L to afford the substrate is also to be inferred from the rate data. For L = P(OCH₂)₃CCH₃, an intermediate of this type, cis-DTN)W(CO)₄(L) was isolated and characterized, and the kinetics of its formation and decomposition were studied. The data provide conclusive evidence for the operation of the ring-opening mechanism in these Systems.     

Synthesis and characterization of T[Ni(CN)4]·2pyz with T=Fe, Ni; pyz=pyrazine: Formation of T-pyz-Ni bridges

The formation of T-pyz-Ni bridges (pyz=pyrazine) in the T[Ni(CN)₄]·2pyz series is known for T=Mn, Zn, Cd and Co but not with T=Fe, Ni. In this contribution the existence of such bridges also for T=Fe, Ni is discussed. The obtained pillared solids, T[Ni(CN)₄]·2pyz, were characterized from XRD, TG, UV-Vis, IR, Raman, Mössbauer and magnetic data. Their crystal structures were refined in the orthorhombic Pmna space group from XRD powder patterns. The structural behavior of these solids on cooling down to 77 K was also studied. In the 180-200 K temperature range the occurrence of a structural transition to a monoclinic structure (P2₁/c space group) was observed. No temperature induced spin transition was observed for Fe[Ni(CN)₄]·2pyz. The iron (II) was found to be in high spin electronic state and this configuration is preserved on cooling down to 2 K. The magnetic data indicate the occurrence of a low temperature weak anti-ferromagnetic interaction between T metal centers within the T[Ni(CN)₄] layer. In the paramagnetic region for Ni[Ni(CN)₄]·2pyz, a reversible temperature induced spin transition for the inner Ni atom was detected.     

Substitution kinetics of W(CO)5(η-bis(trimethylsilyl)ethyne) with triphenylbismuthine

The labile complex W(CO)₅(η²-btmse) undergoes replacement of bis(trimethylsilyl)ethyne, btmse, by triphenylbismuthine in cyclohexane solution at an observable rate in the temperature range of 35-50 °C yielding almost solely W(CO)₅(BiPh₃) as the final product. The kinetics of this substitution reaction was studied in cyclohexane solution by quantitative FT-IR spectroscopy. The substitution reaction obeys a pseudo-first-order kinetics with respect to the concentration of the starting complex. The observed rate constant, k_obs, was determined at four different temperatures and three different concentrations of the entering ligand BiPh₃ in the range 16.8-65.4 mM. From the evaluation of kinetic data a possible reaction mechanism was proposed in which the rate determining step is the cleavage of metal-alkyne bond in the complex W(CO)₅(η²-btmse). A rate law was derived from the proposed mechanism. From the dependence of k_obs on the entering ligand concentration, the rate constant k₁ for the rate determining step was estimated at all temperatures. The activation enthalpy (106 ± 2 kJ mol⁻¹) and the activation entropy (111 ± 6 J K⁻¹ mol⁻¹) were determined for this rate determining step from the evaluation of k₁ values at different temperatures. The large positive value of the activation entropy is consistent with the dissociative nature of reaction. The large value of the activation enthalpy, close to the calculated tungsten-alkyne bond dissociation energy, also supports this dissociative rate-determining step of the substitution reaction.     

Dimeric and trimeric diorganosilicon chalcogenides (PhRSiE)2,3 (E = S, Se, Te; R = Ph, Me)

Ph₂SiCl₂ and PhMeSiCl₂ react with Li₂E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE)₃ (R = Ph: 1a-3a, R = Me: cis/trans-4a (E = S), cis/trans-5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE)₂ (R = Ph: 1b-2b, R = Me: cis/trans-4b (E = S), cis/trans-5b (E = Se)) have been observed as by-products. 1a-5b have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ⁷⁷Se, ¹²⁵Te). Four- and six-membered ring compounds differ significantly in ²⁹Si and ⁷⁷Se chemical shifts as well as in the value of ¹J_SiSe.The molecular structures of 2a, 3a and trans-5a reported in this paper are the first examples of compounds with unfused six-membered rings Si₃E₃ (E = Se, Te). The Si₃E₃ rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te-Te contact of 3.858 Å which yields a dimerization in the solid state.     

The nature of the lowest excited state and photosubstitution reactivity of tetracarbonyl-1,10-phenanthrolinetungsten(0) and related complexes

Absorption and emission spectral studies of M(CO)₄L complexes (M = Cr Mo, W; L = 2,2′-bipyridine, 1,10-phenanthroline, 5-CH₃-, 5-Cl-, 5-Br-, 5-NO₂-1,10-phenanthroline) have been carried out and reveal that the lowest excited state in every case is charge-transfer (CT) in character, M→ CT in absorption, and in no case do the ligand field (LF) excited states cross below the CT state. Minimum energies of the LF states have been established by the spectroscopic study of cis-bis(pyridine)- and cis-bis(aliphatic amine)-tetracarbonylmetal(0) complexes which all have LF lowest excited states for M = Mo, W. For the M(CO)₄L complexes emission is detectable for M = Mo or W and occurs in the range 14.40-15.66 kK with lifetimes of 7.9-13.3 μsec and quantum yields of 0.02–0.09 all in EPA solution at 77 K. For the bis-pyridine and -aliphatic amine complexes emission occurs only from the W complexes and is of the order of 3.0–4.0 kK higher in energy than for the M(CO)₄L complexes. Photosubstitution of pyridine is efficient in cis-W(CO)₄(py)₂ (py = pyridine): Φ_436nm = 0.23; Φ_405nm = 0.27; and Φ_366nm = 0.23. The M(CO)₄L complexes have strongly wavelength dependent, but modest, quantum yields for CO substitution and show that the lowest CT state is unreactive. Typical values for CO substitution for M = W and L = 1,10-phenanthroline are: Φ_436nm = 1.6 × 10^?4; Φ_405nm = 1.2 × 10^?3; Φ_366nm = 9.2 × 10^?3; and Φ_313nm = 2.2 × 10^?2.     

Synthesis and electrochemistry of Group 6 tetracarbonyl (N,N′-bis(ferrocenylmethylene)ethylenediamine)metal(0) complexes

Thermal substitution reaction of Cr(CO)₄(η^2:2-1,5-cyclooctadiene), Mo(CO)₄(η^2:2-norbornadiene), and W(CO)₅(η²-bis(trimethylsilyl)ethyne) with N,N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO)₄(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO)₅(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO)₄(bfeda). The electrochemical behavior of the M(CO)₄(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH₂Cl₂ solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO)₄(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO)₄(bfeda) and W(CO)₄(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom.     

Rhenium(I) and technetium(I) fac-M(NSO)(CO)3 (M = Re,Tc) tricarbonyl complexes,with a tridentate NSO bifunctional agent: Synthesis,structural characterization,and radiochemistry

The synthesis and structural characterization of the neutral rhenium complex fac-[Re(NSO)(CO)₃], Re-1, where (NSO) is a tridentate bifunctional chelating agent, 3-(carboxymethylthio)-3-(1H-imidazol-4-yl)propanoic acid (1), is presented. The complex crystallized from methanol–water and its structure was assigned by IR and ¹H, ¹³C NMR spectroscopies and X-ray crystallography. Furthermore, the analogous technetium complex fac-[^99mTc(NSO)(CO)₃], ^99mTc-1, was synthesized in high yield by reacting ligand 1 with the fac-[^99mTc(OH₂)₃(CO)₃]⁺ precursor for 30 min at 85 °C. The tracer complex was found to be more than 95% stable in the L-histidine challenge experiment. Our data indicate that the bifunctional NSO chelating agent 1 can be successfully applied for the development of potential ^99mTc-radiopharmaceuticals.     

Cyclic carbene formation through alkyl migration to molybdenum coordinated isonitrile. Synthesis and X-ray structure of cis-MoI {C(NMe)[CH2]2CH2} (CO)2(η-C5H5). An example of a sterically blocked cis-trans isomerisation for the [Mo(X)(L)(CO)2(η-C5H5)] system

Treatment of Mo(CNMe)(CO)₂(η-C₅H₅)^? with I[CH₂]₃I in tetrahydrofuran affords the carbene complex cis-MoI{C(NMe)[CH₂[CH₂} (CO)₂ (η-C₅H₅), which has been characterised by X-ray crystallography. This complex does not isomerise to the corresponding trans isomer, as might have been expected by analogy with related 2-oxacyclopentylidene systems.     

Reductive elimination of halogens assisted by phosphine ligands in Fe(CO)4X2 (X = I, Br) complexes

Fe(CO)₄X₂ complexes [X = I (1), Br(1′)] react with phosphine ligands L (L = PMe₃, PEt₃, PMe₂Ph, PMePh₂, PPh₃) via a two-step mechanism: in the first step fac-Fe(CO)₃LX₂ complexes are formed; in the second step two parallel pathways, a and b, are observed; in pathway a, reductive elimination with formation of equimolar amounts of Fe(CO)₃L₂ (5) and phosphonium salts [LX]⁺X⁻ is observed; in pathway b, disubstituted dihalide complexes cis,trans,cis-Fe(CO)₂L₂X₂ are formed. The relative weights of pathways a and b depend on the basicity, steric hindrance and concentration of ligand L, on the nature of the halogen and on temperature. A radical mechanism which accounts for most of the experimental results is proposed.     

Branched and dendritic metallo-carbosiloxanes with OCH2PPh2MLn end-grafted units

A straightforward method for the preparation of metallo carbosiloxanes of type Si(OCH₂CH₂CH₂SiMe₂[OCH₂PPh₂M(CO)_n])₄ (n = 3, M = Ni, 7a; n = 4, M = Fe, 7b; n = 5: M = Mo, 7c; M = W, 7d), Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₄ (8) and Me₂Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₂ (11) is described. The reaction of Si(OCH₂CH₂CH₂SiMeXCl)₄ (1: X = Me, 2: X = Cl) or Me₂Si(OCH₂CH₂CH₂SiMeCl₂)₂ (9) with HOCH₂PPh₂ (3) produces Si(OCH₂CH₂CH₂SiMe₂(OCH₂PPh₂))₄ (4), Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₄ (5) or Me₂Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₂ (10) in presence of DABCO. Treatment of the latter molecules with Ni(CO)₄ (6a), Fe₂(CO)₉ (6b), M(CO)₅(Thf) (6c: M = Mo; 6d: M = W), respectively, gives the title compounds 7a-7d, 8 and 11 in which the PPh₂ groups are datively bound to a 16-valence-electron metal carbonyl fragment.The formation of analytical pure and uniform branched and dendritic metallo carbosiloxanes is based on elemental analysis, and IR, ¹H, ¹³C{¹H}, ²⁹Si{¹H} and ³¹P{¹H} NMR spectroscopic studies. In addition, ESI-TOF mass spectrometric studies were carried out.     

Density functional theory study on structural isomers and bonding of model complexes M(CO)5(BH3 · PH3) (M = Cr, Mo, W) and W(CO)5(BH3 · AH3) (A = N, P, As, Sb)

The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)₅(BH₃ · AH₃) and M(CO)₅(BH₃ · PH₃) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η¹, with C₁ point group; (b) in all complexes, the η¹ isomer with C_S symmetry on potential energy surface is the transition state for oscillating borane; (c) the η² isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)₅(BH₃ · AH₃), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)₅(BH₃ · PH₃), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo.     

Synthesis of the pentacarbonyl(chalcocarbonyl)chromium(0) complexes,Cr(CO)5(CX) (X = S,Se)

The arene complexes, (η⁶-C₆H₆)Cr(CO)₂(CX) (X = S, Se), react with excess CO gas under pressure in tetrahydrofuran at about 60° C to produce the Cr(CO)₅(CX) complexes in high yield. The IR and NMR (¹³C and ¹⁷O) spectra of these complexes are in complete accord with the expected C_4v molecular symmetry. Like the analogous W(CO)₅(CS) complex, both compounds react with cyclohexylamine to give Cr(CO)₅(CNC₆H₁₁). However, while W(CO)₅(CS) undergoes stereospecific CO substitution with halide ions (Y^? to form trans-[W(CO)₄(CS)Y]^?, the two chromium chalcocarbonyl complexes apparently undergo both CO and CX substitution to afford mixtures of [Cr(CO)₅Y]^? and trans-[Cr(CO)₄(CX)Y]^?.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

Kinetic studies of the reactions of the carbene complex W(CO)5[C(SCH3)2] with phosphines to form phosphorane complexes W(CO)5[(CH3S)2C-PR3] and the synthesis of some cyclic phosphorane complexes

The dithiocarbene complex W(CO)₅[C(SCH₃)₂ reacts with tertiary phosphines, PPh₂CH₃, PPh(CH₃)₂, P(C₂H₅)₃ and P(OCH₃)₃ to form the phosphorane complexes W(CO)₅[CH₃S)₂C-PR₃] and with HPPh₂ to form the phosphine complex W(CO)₅[PPh₂[CH(SCH₃)₂]. Kinetic studies of both types of reactions show that their rates are first order each in W(CO)₅[C(SCH₃)₂] and in the phosphorus ligand. A mechanism involving rate determining phosphorus attack at the carbene carbon followed by rapid rearrangement to the product is consistent with this rate law. Rate constants for the reactions increase with increasing nucleophilicities of the phosphines: P(OCH₃)₃ < PPh₂H < PPh₂C_H3 ? PPh(CH₃)₂ < P(C₂H₅)₃. The ΔH values decrease (P(OCH₃)₃ > PPh₂H > PPh₂(CH₃) > PPh(CH₃)₂ > P(C₂H₅)₃) as the nucleophilicities of the phosphines increase. The ΔS values (≈-30 e.u.) remain essentially constant for all the reactions. The cyclic dithiorcarbenes W(CO)₅[CS(CH₂)_nS], wheren- 3 or 4, react with PPh₂(CH₃) to form the cyclic phosphorane complexes, W(CO)₅[S(CH₂)_nSC-PPh₂(CH₃)]. The 6- and 7- membered cyclic dithiocarbenes also react with PPh₂H to form the phosphine complexes, W(CO)₅ {PPh₂- [CS(CH₂)_nS(H)]}.     

Activation of the Si-H bond of Et2SiH2 in photochemical reaction with W(CO)6: Spectroscopic characterization of intermediate W-Si compounds and the revisited crystal structure of the bis{(μ-η-hydridodiethylsilyl)tetracarbonyltungsten(I)} complex [{W(μ-η-H-SiEt2)(CO)4}2]

The photochemical reaction of W(CO)₆ with diethylsilane has been used to generate new tungsten-silicon compounds varying in stability. The initially formed η²-silane intermediate complex [W(CO)₅(η²-H-SiHEt₂)], characterized by two equal-intensity doublets with ²J_H-H = 10 Hz at δ = 5.10 (¹J_Si-H = 217 Hz) and δ = −8.05 (¹J_W-H = 38 Hz, ¹J_Si-H = 93 Hz), was detected by the ¹H NMR spectroscopy (methylcyclohexane-d₁₄, −10 °C). The η²-silane complex was converted in the dark to give more stable species. One of them was characterized by two equal-intensity proton signals observed as doublets with ²J_H-H = 5.2 Hz at δ = −8.25 and −10.39 ppm. The singlet proton resonance at δ = −9.31 flanked by ²⁹Si and ¹⁸³W satellites (¹J_Si-H = 43 Hz, ²J_Si-H = 34 Hz, ¹J_W-H = 40 Hz) was assigned to the agostic proton of the W(η²-H-SiEt₂) group in the most stable compound isolated from the photochemical reaction products in crystalline form. The molecular structure of the bis{(μ-η²-hydridodiethylsilyl)tetracarbonyltungsten(I)} complex [{W(μ-η²-H-SiEt₂)(CO)₄}₂] was established by single-crystal X-ray diffraction studies. The tungsten hydride observed in the ¹H NMR spectrum at δ = −9.31 was located in the structure at a chemically reasonable position between the W and Si atoms of the W-Si bond of the bridging silyl ligand. The reactivity of photochemically generated W-Si compounds towards norbornene, cyclopentene, diphenylacetylene, acetone, and water was studied. As was observed by IR and NMR spectroscopy, the η²-silane ligand in the complex [W(CO)₅(η²-H-SiHEt₂)] is very easily replaced by an η²-olefin or η²-alkyne ligand.     

Synthesis, structure, properties, volatility, and thermal stability of molybdenum(II) and tungsten(II) complexes containing allyl, carbonyl, and pyrazolate or amidinate ligands

Treatment of M(allyl)(Cl)(CO)₂(py)₂ (M = Mo, W) with 1 equiv. of potassium pyrazolates in tetrahydrofuran at −78 °C afforded M(allyl)(R₂pz)(CO)₂(py)_n (R₂pz = 3,5-disubstituted pyrazolate; n = 1, 2) in 68-81% yields. X-ray crystal structure analyses of Mo(allyl)((CF₃)₂pz)(CO)₂(py)₂ and W(allyl)(tBu₂pz)(CO)₂(py) revealed η¹- and η²-coordination of the (CF₃)₂pz and tBu₂pz ligands, respectively. Analogous treatment of Mo(allyl)(Cl)(CO)₂(NCCH₃)₂ with 1 equiv. of tBu₂pzK in tetrahydrofuran at −78 °C afforded [Mo(allyl)(tBu₂pz)(CO)₂]₂ in 79% yield. An X-ray crystal structure analysis of [Mo(allyl)(tBu₂pz)(CO)₂]₂ showed a dimeric structure bridged by two μ-η²:η¹-tBu₂pz ligands. Treatment of M(allyl)(Cl)(CO)₂(py)₂ with 1 equiv. of lithium 1,3-diisopropylacetamidinate or lithium 1,3-di-tert-butylacetamidinate in diethyl ether at −78 °C afforded M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) and M(allyl)(tBuNC(Me)NtBu)(CO)₂(py), respectively, in 68-78% yields. The new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) adopt pseudo-octahedral geometry about the metal centers, with the 1,3-diisopropylacetamidate ligand nitrogen atoms spanning one axial site and one equatorial site of the octahedron. By contrast, M(allyl)(tBuNC(Me)NtBu)(CO)₂(py) adopt pseudo-octahedral structures in which the two 1,3-di-tert-butylacetamidinate ligand nitrogen atoms span two equatorial coordination sites. Sublimation of M(allyl)(tBuNC(Me)NtBu)-(CO)₂(py) at 105 °C/0.03 Torr afforded ?7% yields of M(allyl)(tBuNC(Me)NtBu)(CO)₂, along with sublimed M(allyl)(tBuNC(Me)NtBu)(CO)₂(py). W(allyl)(tBuNC(Me)NtBu)(CO)₂ exists in the solid state as a 16-electron complex with distorted square pyramidal geometry. Many of the new complexes undergo dynamic ligand site exchange in solution, and these processes were probed by variable temperature ¹H NMR spectroscopy. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use as precursors in thin film growth experiments.