M-P versus M=M bonds as protonation sites in the organophosphide-bridged complexes [M2Cp2(mu-PR2)(mu-PR'2)(CO)2], (M = Mo, W; R, R' = Ph, Et, Cy)

The unsaturated complexes [W2Cp2(mu-PR2)(mu-PR'2)(CO)2] (Cp = eta5-C5H5; R = R' = Ph, Et; R = Et, R' = Ph) react with HBF4.OEt2 at 243 K in dichloromethane solution to give the corresponding complexes [W2Cp2(H)(mu-PR2)(mu-PR'2)(CO)2]BF4, which contain a terminal hydride ligand. The latter rearrange at room temperature to give [W2Cp2(mu-H)(mu-PR2)(mu-PR'2)(CO)2]BF4, which display a bridging hydride and carbonyl ligands arranged parallel to each other (W-W = 2.7589(8) A when R = R' = Ph). This explains why the removal of a proton from the latter gives first the unstable isomer cis-[W2Cp2(mu-PPh2)2(CO)2]. The molybdenum complex [Mo2Cp2(mu-PPh2)2(CO)2] behaves similarly, and thus the thermally unstable new complexes [Mo2Cp2(H)(mu-PPh2)2(CO)2]BF4 and cis-[Mo2Cp2(mu-PPh2)2(CO)2] could be characterized. In contrast, related dimolybdenum complexes having electron-rich phosphide ligands behave differently. Thus, the complexes [Mo2Cp2(mu-PR2)2(CO)2] (R = Cy, Et) react with HBF4.OEt2 to give first the agostic type phosphine-bridged complexes [Mo2Cp2(mu-PR2)(mu-kappa2-HPR2)(CO)2]BF4 (Mo-Mo = 2.748(4) A for R = Cy). These complexes experience intramolecular exchange of the agostic H atom between the two inequivalent P positions and at room-temperature reach a proton-catalyzed equilibrium with their hydride-bridged tautomers [ratio agostic/hydride = 10 (R = Cy), 30 (R = Et)]. The mixed-phosphide complex [Mo2Cp2(mu-PCy2)(mu-PPh2)(CO)2] behaves similarly, except that protonation now occurs specifically at the dicyclohexylphosphide ligand [ratio agostic/hydride = 0.5]. The reaction of the agostic complex [Mo2Cp2(mu-PCy2)(mu-kappa2-HPCy2)(CO)2]BF4 with CN(t)Bu gave mono- or disubstituted hydride derivatives [Mo2Cp2(mu-H)(mu-PCy2)2(CO)2-x(CNtBu)x]BF4 (Mo-Mo = 2.7901(7) A for x = 1). The photochemical removal of a CO ligand from the agostic complex also gives a hydride derivative, the triply bonded complex [Mo2Cp2(H)(mu-PCy2)2(CO)]BF4 (Mo-Mo = 2.537(2) A). Protonation of [Mo2Cp2(mu-PCy2)2(mu-CO)] gives the hydroxycarbyne derivative [Mo2Cp2(mu-COH)(mu-PCy2)2]BF4, which does not transform into its hydride isomer.     

Über den Phosphandiyl‐Transfer von invers‐polarisierten Phosphaalkenen R1P=C(NMe2)2 (R1 = tBu,Cy, Ph,H) auf Phospheniumkomplexe [(η5‐C5H5)(CO)2M=P(R2)R3] (R2 = R3 = Ph; R2 = tBu,R3 = H; R2 = Ph,R3 = N(SiMe3)2)

Phosphanediyl Transfer from Inversely Polarized Phosphaalkenes R¹P=C(NMe₂)₂ (R¹ = tBu, Cy, Ph, H) onto Phosphenium Complexes [(η⁵‐C₅H₅)(CO)₂M=P(R²)R³] (R² = R³ = Ph; R² = tBu, R³ = H; R² = Ph, R³ = N(SiMe₃)₂) Reaction of the freshly prepared phosphenium tungsten complex [(η⁵‐C₅H₅)(CO)₂W=PPh₂] ( 3 ) with the inversely polarized phosphaalkenes RP=C(NMe₂)₂ ( 1 ) ( a : R = tBu; b : Cy; c : Ph) led to the η²‐diphosphanyl complexes ( 9a‐c ) which were isolated by column chromatography as yellow crystals in 24‐30 % yield. Similarly, phosphenium complexes [(η⁵‐C₅H₅)(CO)₂M=P(H)tBu] (M = W ( 6 ); Mo ( 8 )) were converted into (M = W ( 11 ); Mo ( 12 )) by the formal abstraction of the phosphanediyl [PtBu] from 1a . Treatment of [(η⁵‐C₅H₅)(CO)₂W=P(Ph)N(SiMe₃)₂] ( 4 ) with HP=C(NMe₂)₂ ( 1d ) gave rise to the formation of yellow crystalline ( 10 ). The products were characterized by elemental analyses and spectra (IR, ¹H, ¹³C‐, ³¹P‐NMR, MS). The molecular structure of compound 10 was elucidated by an X‐ray diffraction analysis.     

Reactivity of the inversely polarized phosphaalkenes RP=C(NMe2)2 (R = tBu, Me3Si, H) towards arylcarbene complexes [(CO)5M=C(oEt)Ar] (Ar= Ph, M = Cr, W; Ar = 2-MeC6H4, 2-MeOC6H4, M = W)

The reaction of the arylated Fischer carbene complexes [(CO)5M=C(OEt)Ar] (Ar=Ph; M = Cr, W; 2-MeC6H4; 2-MeOC6H; M = W) with the phosphaalkenes RP=C(NMe2), (R=tBu, SiMe3) afforded the novel phosphaalkene complexes [[RP=C(OEt)Ar]M(CO)5] in addition to the compounds [(RP=C(NMe2)2]M(CO)5]. Only in the case of the R = SiMe3 (E/Z) mixtures of the metathesis products were obtained. The bis(dimethylamino)methylene unit of the phosphaalkene precursor was incorporated in olefins of the type (Me2N)2C=C(OEt)(Ar). Treatment of [(CO)5W=C(OEt)(2-MeOC6H4)] with HP=C(NMe2)2 gave rise to the formation of an E/Z mixture of [[(Me2N)2CH-P=C(OEt)(2-MeOC6H4)]W(CO)5] the organophosphorus ligand of which formally results from a combination of the carbene ligand and the phosphanediyl [P-CH(NMe2)2]. The reactions reported here strongly depend on an inverse distribution of alpha-electron density in the phosphaalkene precursors (Pdelta Cdelta+), which renders these molecules powerfu] nucleophiles.     

Metallkomplexe von Phenylenbistriazeniden: Synthese und Kristallstrukturen von [Cp(CO)2M]2(1,2-PhN3C6H4N3Ph) (M = Mo,W)

Metal Complexes of Phenylenebistriazenides: Synthesis and Crystal Structures of [Cp(CO)₂M]₂(1,2-PhN₃C₆H₄N₃Ph) (M = Mo, W) [Cp(CO)₂M]₂(1,2-PhN₃C₆H₄N₃Ph) [(M = Mo( 1 ), M = W( 2 )] is formed in the reaction of Cp(CO)₃MCl with PhN₃(H)C₆H₄N₃(H)Ph and C₂H₅ONa in a THF/ethanol mixture. 1 crystallizes from toluene as dark red crystals (triclinic, P1 , a = 1 499.3(9) pm, b = 1 734.0(7) pm, c = 1 852.8(8) pm, α = 66.84(3)°, β = 78.25(4)°, γ = 77.19(4)°). The unit cell contains four complexes with two independent complexes in the asymmetric unit, and eight solvent molecules. 2 crystallizes from THF as yellow crystals free from solvent molecules (triclinic, P1 , a = 979.0(5) pm, b = 1 152.8(5) pm, c = 1 475.8(5) pm, α = 98.26(4)°, β = 104.93(4)°, γ = 101.03(4)°, Z = 2). 1 and 2 are discrete molecular complexes with a 1,2-bis(phenyltriazenido)phenylligand, (PhN₃C₆H₄N₃Ph)^2?, chelating the metal atoms of two Cp(CO)₂M units with the N atoms N1 and N3 of both N₃ groups. Due to the sterical pretension of the Cp(CO)₂M units the phenylenebistriazenido ligand deviates strongly from planarity that is found in the metal complexes characterized so far.     

Cluster chemistry: XXXVIII. Reactions between M(C2R)(PR′3 (M = Cu,Ag, Au; R = Ph,C6F5; R′ = Me Ph) and H2Os3(CO)10: X-ray structures of Os3Au(μ-CHCHR)(CO)10(PPh3) (R = Ph and C6F5)

The reactions of Os₃(μ-H)₂(CO)₁₀ with a series of Group IB metal acetylide-tertiary phosphine complexes are described. Whereas the compounds M(C₂C₆F₅)(PPh₃) (M = Cu, Ag, Au) afforded the complexes MOs₃(μ-CHCHC₆F₅)(CO)₁₀(PPh₃) cleanly and in high yield, complex mixtures of products were obtained from reactions of the analogous phenylacetylides. The complexes MOs₃(μ-CHCHPh)(CO)₁₀(PPh₃), MOs₃(μ-CHCHPh)(CO)₉(PPh₃)₂ and MOs₃(μ-H)(CO)₁₀(PPh₃) (of known structure), and MOs₃(μ-CHCHPh)(CO)₉(PPh₃)₂ and HMOs₃(CHCPh)(CO)₈ (of unknown structure) were characterised; Au(C₂Ph)(PMe₃) afforded similar derivatives. The reactions proceed by oxidative-addition and hydrogen migration steps; MP bond cleavage reactions also occur to a small extent. The molecular structures of AuOs₃(μ-CHCHC₆R₅)(CO)₁₀(PPh₃) (R = F or H) were determined by X-ray analyses. For R = F, crystals are triclinic, space group P$\text{1}$ with a 9.081(2), b 13.291(2), c 17.419(2) Å, α 84.49(1), β 76.20(2), γ 75.81(2)° and Z = 2; 4622 observed data [I > 2.5σ(I)] were refined to R = 0.027, R_W = 0.031. For R = H, crystals are triclinic, space group P$\text{1}$, with a 9.403(4), b 13.448(3), c 13.774(4) Å, α 83.34(2), β 88.66(3), γ 70.21(3)°, and Z = 2; 4405 observed data [I > 2.5σ(I)] were refined to R = 0.030, R_W = 0.033. The two molecules differ in the orientation of the Ph rings of the PPh₃ groups, but are otherwise similar to Os₃(μ-H)(μ-CHCHBu^t)(CO)₁₀ with the μ-H ligand replaced by the isolobal μ-Au(PPh₃) group.     

The course of (R2R'SiO)3TaCl2 (R = tBu, R' = H, Me, Ph, tBu (silox); R = iPr, R' = tBu, iPr) reduction is dependent on siloxide size

Various sized siloxides (Cy(3)SiO > (t)Bu(3)SiO > (t)Bu(2)PhSiO > (t)Bu(2)MeSiO approximately (i)Pr(2)(t)BuSiO > (i)Pr(3)SiO > (t)Bu(2)HSiO) were used to make (R(2)R'SiO)(3)TaCl(2) (R = (t)Bu, R' = H (1-H), Me (1-Me), Ph (1-Ph), (t)Bu (1); R = (i)Pr, R' = (t)Bu (1-(i)Pr(2)); R = R' = (i)Pr (1-(i)Pr(3)); R = R' = (c)Hex (Cy)). Product analyses of sodium amalgam reductions of several dichlorides suggest that [(R(2)R'SiO)(3)Ta](2)(mu-Cl)(2) may be a common intermediate. When the siloxide is large (1-(t)Bu), formation of the Ta(III) species ((t)Bu(3)SiO)(3)Ta (6) occurs via disproportionation. When the siloxide is small, the Ta(IV) intermediate is stable (e.g., [((i)Pr(3)SiO)(3)Ta](2)(mu-Cl)(2) (2)), and when intermediate sized siloxides are used, solvent bond activation via unstable Ta(III) tris-siloxides is proposed to occur. Under hydrogen, reductions of 1-Me and 1-Ph provide Ta(IV) and Ta(V) hydrides [((t)Bu(2)MeSiO)(3)Ta](2)(micro-H)(2) (4-Me) and ((t)Bu(2)PhSiO)(3)TaH(2) (7-Ph), respectively.     

The elusive 16-electron Cp*M(NO)Me(2)(M = Mo, W) complexes and their spontaneous conversions to Cp*M(NMe)(O)Me isomers.

Treatment of [Cp*Mo(NO)Cl(mu-Cl)](2) with magnesium (Me(2)Mg.dioxane, MeMgCl) or aluminum (Me(3)Al) methylating reagents affords the known compound [Cp*Mo(NO)Me(mu-Cl)](2) (1). Similar treatment of the dichloro precursor with MeLi in ethereal solvents generates an equimolar mixture of 1 and the trimethyl "ate" complex, Cp*MoMe(3)(NO-Li(OEt(2)(n)), (2-Et(2)O). Reaction of 2-Et(2)O with a source of [Me](+) forms Cp*MoMe(3)(=N-OMe)(3), a rare terminal alkoxylimido complex. Metathesis of the chloro ligands of [Cp*Mo(NO)Cl(mu-Cl)](2) by MeLi in toluene at low temperatures produces the target dimethyl complex, Cp*Mo(NO)Me(2) (4), in 75% isolated yield. In solution, 4 is predominantly a monomeric species, whereas in the solid state it adopts a dimeric or oligomeric structure containing isonitrosyl bridges as indicated by IR and (15)N/(13)C NMR spectroscopies. Hydrolysis of 4 affords meso- and rac-[Cp*Mo(NO)Me](2)(mu-O) (5), and the reactions of 4 with a range of Lewis bases, L, to form the 18e adducts Cp*Mo(NO)(L)Me(2) (e.g., Cp*Mo(NO)(PMe(3))Me(2) (7)), have established it to be the most electrophilic complex of its family. Acidolysis of the methyl groups of 4 is also facile. Most notably, 4 is thermally unstable in solution and undergoes isomerization via nitrosyl N-O bond cleavage to its oxo(imido) form, Cp*Mo(NMe)(O)Me (11), which is isolable from the final reaction mixture as the mu-oxo-bridged adduct formed by 4 and 11, i.e., Cp*Mo(NO)Me(2)(mu-O)Cp*Mo(NMe)Me (4 <-- 11). The rate of this isomerization is significantly faster for the tungsten dimethyl complex; hence, Cp*W(NO)Me(2) (12) is not isolable free of a supporting donor interaction and can only be isolated as Cp*W(NO)Me(2)(mu-O)Cp*W(NMe)Me (12 <-- 13) or Cp*W(NO)Me(2)(PMe(3)) (14) adducts.     

A metallocene-complexed dibismuthene: Cp2Zr(BiR)2 (Cp = C5H5; R = C6H3-2,6-Mes2)

The zirconocene-complexed dibismuthene, Cp2Zr(BiR)2 (Cp = C5H5; R = C6H3-2,6-Mes2), was prepared by the reaction of sodium metal with Cp2ZrCl2 and RBiCl2. The air- and moisture-sensitive dark reddish/brown compound is the first organometallic compound containing Bi-Zr bonds and the only example of a ZrBi2 ring. Moreover, our computations on associated model systems offer insight into the nature of the interaction of the heaviest dipnictene with a metallocene center.     

Organometallic Niobium and Tantalum Complexes with Primary Phosphine Ligands: Syntheses and Molecular Structures of [Cp*MCl4(PH2R)] (M = Nb,Ta; Cp* = C5Me5;R = But,Ad, Cy,Ph, 2, 4, 6‐Me3C6H2 (Mes))

The reaction of [Cp*MCl₄] (M = Nb, Ta; Cp* = C₅Me₅) with PH₂R in toluene at room temperature gives the primary phosphine complexes [Cp*MCl₄(PH₂R)] [Cp* = C₅Me₅; M = Nb: R = Bu^t ( 1a ), Ad ( 2a ), Cy ( 3a ), Ph ( 4a ), 2, 4, 6‐Me₃C₆H₂ (Mes) ( 5a ); M = Ta: R = Bu^t ( 1b ), Ad ( 2b ), Cy ( 3b ), Ph ( 4b ), Mes ( 5b )] in high yield. 1—5 were characterized spectroscopically (NMR, IR, MS) and by crystal structure determinations. The starting material [Cp*TaCl₄] is monomeric in the solid state, as shown by crystal structure determination.     

Steric and electronic effects on the heterolytic H2‐splitting by phosphine‐boranes R3B/PR′3 (R = C6F5, Ph; R′ = C6H2Me3, tBu,Ph, C6F5, Me,H): A computational study

The steric and electronic effects exerted by the substituents R/R′ on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃ [R = C₆F₅ ( 1 ), Ph ( 2 ); R′ = C₆H₂Me₃ ( a ), tBu ( b ), Ph ( c ), C₆F₅ ( d ), Me ( e ), H ( f )] have been studied by performing quantum mechanical density functional theory and RI‐MP2 calculations. Energy decomposition analyses based on the block‐localized wavefunction method show that the nature of the interaction between R₃B and PR′₃ is strongly dependent on the B? P distance. With short B? P distances (～2.1 Å), the strength of Lewis pairs results from the balance among various energy terms, and both strong and weak dative bonds can be found in this group. However, at long B? P distances (>4.0 Å), the correlation and dispersion energy (ΔE_corr) dominates. In other words, the van der Waals (vdW) interaction rules these weakly bound complexes. No ion‐pair structures of 1f and 2c – 2f can be located as they instantly converge to vdW complexes R₃B···H₂···PR′₃. We thus propose a model, which predicts that when the sum (E_hp) of the hydride affinity (HA) of BR₃ and the proton affinity (PA) of PR′₃ is higher than 340.0 kcal/mol, the ion‐pair [R₃BH^?][HPR′] can be observed, whereas with E_hp below this value, the ion pair would instantly undergo the combination of proton and hydride with the release of H₂. The overall reaction energies ( 1a – 1e and 2a – 2b ) can be best described by a fitting equation with HA(BR₃), PA(PR′₃), and the binding energy ΔE_b(BR₃/PR′₃) as predictor variables: ΔE_R([R₃BH^?][HPR′]) = ?0.779HA(BR₃) ? 0.695PA(PR′₃) ? 1.331 ΔE (BR₃/PR′₃) + 245.3 kcal/mol. The fitting equation provides quantitative insights into the steric and electronic effects on the thermodynamic aspects of the heterolytic H₂‐splitting reactions. The electronic effects are reflected by HA(BR₃) and PA(PR′₃), and ΔE_b can be significantly influenced by the steric overcrowding. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Photoinduzierte und thermische reaktionen der übergangsmetallethylverbindungen CpM(CO)3Et (Cp = η5-cyclopentadienyl; Et = ethyl; M = Mo,W)

In the compounds CpM(CO)₃Et (M = Mo, W) the metal-ethyl σ-bond is photolabile. Upon irradiation of a solution of CpM(CO)₃Et with UV light mainly [CpM(CO)₃]₂, CpM(CO)₃H, ethane, and ethylene are produced. Formation of CpM(CO)₃H is indicative of a β-elimination pathway for the photo-induced degradation. In the presence of trimethylphosphane (L) UV-irradiation of a solution of CpM(CO)₃Et leads to the products Cp(CO)(L)₂MM-(CO)₃Cp, CpM(CO)₂(L)Et and CpM(CO)₂(L)H, while the thermal reaction produces the propionyl complexes CpM(CO)₂(L)(COEt).     

Alternativ-Liganden. VIII. Chelatkomplexe des Typs M(CO)4(Me2XGeMe2CH2X′Me2) (M = Cr,Mo, W; X,X′ = N,P, As; Me = CH3)

Chelate Complexes of the Type M(CO)₄(Me₂XGeMe₂CH₂X′Me₂) (M) = Cr, Mo, W; X, X′ = N, P, As; Me = CH₃) The ligands (Me₂)XGeMe₂CH₂X′Me₂ (M) = Cr, Mo, W) react with M(CO)₄norbor (norbor = Norbornadiene) (M = Cr, Mo, W) yielding the chelate complexes M(CO)₄(Me)₂XGeMe₂CH₂X′Me₂). compounds of low thermal stability are formed with the ligands (Me₂NGeMe₂CH₂X′Me₂ because of the weak donor ability of the GeNMe₂ group and with Me₂AsGeMe₂CH₂NMe₂ caused by strong steric ring tension. The new compounds are characterized by analytical and spectroscopic (n.m.r., i.r., m.s.) investigations.     

Photochemical reactions of M(CO)6 (M = Cr,Mo, W) with Ph2P(S)P(S)Ph2

New complexes {M(CO)₄[Ph₂P(S)P(S)Ph₂]} (M = Cr, Mo and W), (1a)–(3a), [(1a), M = Cr; (2a), M = Mo; (3a), M = W] and {M₂(CO)₁₀[-Ph₂P(S)P(S)Ph₂]} (M = Cr, Mo, W), [(1b)–(3b) [(1b), M = Cr; (2b), M = Mo; (3b), M = W]] have been prepared by the photochemical reaction of M(CO)₆ with Ph₂P(S)P(S)Ph₂ and characterized by elemental analyses, f.t.-i.r. and ³¹P-(¹H)-n.m.r. spectroscopy and by FAB-mass spectrometry. The spectra suggest cis-chelate bidentate coordination of the ligand in {M(CO)₄[Ph₂P(S)P(S)Ph₂]} and cis-bridging bidentate coordination of the ligand between two metals in (M = Cr, Mo and W).     

Photochemical reactions of metal carbonyls [M(CO)6 (M = Cr,Mo and W), Re(CO)5Br,Mn(CO)3Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh)

Five new complexes, [M(CO)₅(apmsh)] [M = Cr; (1), Mo; (2), W; (3)], [Re(CO)₄Br(apmsh)] (4) and [Mn(CO)₃(apmsh)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)₆] (M = Cr, Mo and W), [Re(CO)₅Br], and [Mn(CO)₃Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh). The complexes have been characterized by elemental analysis, mass spectrometry, f.t.-i.r. and ¹H spectroscopy. Spectroscopic studies show that apmsh behaves as a monodentate ligand coordinating via the imine N donor atom in [M(CO)₅(apmsh)] (1–4) and as a tridentate ligand in (5).     

Silylchalcogenolates MESiR(t)Bu(2) (M = Na, Cu, Zn, Fe; E = S, Se, Te; R = tBu, Ph) and disilyldichalcogenides tBu2RSiE-ESiRtBu2 (E = S, Se, Te; R = tBu, Ph): synthesis, properties, and structures

The sodium silyl chalcogenolates NaESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te), accessible by the nucleophilic degradation of S, Se, or Te by the sodium silanides NaSiR(t)Bu(2) (R = Ph, (t)Bu), have been characterized by X-ray structure analysis. Protonolysis of the sodium silyl chalcogenolates yields the corresponding chalcogenols. The Cu and Zn chalcogenolates, [Cu(SSiPh(t)Bu(2))](4) and [ZnCl(SSi(t)Bu(3))(THF)](2), have been synthesized by metathesis reactions of CuCl with NaSSiPh(t)Bu(2) and of ZnCl(2) with NaSSi(t)Bu(3), respectively. The solid-state structures of the transition metal thiolates have been determined. The compounds (t)Bu(2)RSiE-ESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te) are accessible via air oxidation. With the exception of (t)Bu(3)SiS-SSi(t)Bu(3), these compounds were analyzed using X-ray crystallography and represent the first structurally characterized silylated heavy dichalcogenides. Oxidative addition of (t)Bu(3)SiTe-TeSi(t)Bu(3) to Fe(CO)(5) yields [Fe(TeSi(t)Bu(3))(CO)(3)](2), which has also been structurally characterized.     

Darstellung und spektroskopische Untersuchungen von M(CO)4L2- und M(CO)3L3-Komplexen (M = Cr,Mo, W; L = Me3SiOCH2PMe2, Me2(CH2CH) SiOCH2PMe2)

Preparation and spectroscopical Investigations of M(CO)₄L₂ and M(CO)₃L₃ Complexes (M = Cr, Mo, W; L = Me₃SiOCH₂PMe₂, Me₂(CH₂?CH)SiOCH₂PMe₂ The coordinating properties of the ligands L¹ (?Me₃SiOCH₂PMe₂) and L² (?Me₂ViSiOCH₂PMe₂)¹) have been studied by synthesis and spectroscopic investigations (IR, NMR, MS) of their complexes M(CO)₄L₂ and M(CO)₃L₃(M = Cr, Mo, W). The complexes are obtained by replacement of norbornadiene (NBD) in M(CO)₄NBD or cycloheptatriene CHT in M(CO)₃CHT. Spectroscopic data (v(CO), δ δ) support the σ-donor/-π-acceptor model of the MP bonds.