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The reaction of Ph2Si(CH2Li)(CH2NC5H10) (2) (CH2NC5H10 = piperidinomethyl) with trans-[PdCl2(SMe2)2] leads to dimeric [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(μ-Cl)]2 (3), where the [CH2SiPh2(CH2NC5H10)-κ²C,N] ligand forms a palladacycle, as revealed by the crystal structure of the transoid isomer. In solution, this chloro-bridged dimer exists as a mixture of the cisoid and the transoid isomer. Monodentate ligands cleave the chloro bridges of dimer 3 to give compounds of the type [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}ClL] [L = PPh3 (4), PMe3 (5), CN^tBu (6), 4-methylpyridine (4-MePy) (7), tetrahydrothiophene (tht) (8), SMe2 (9)], where the incoming ligand and the metalated carbon center are coordinated cis. The tetrafluoroborate salt of the cationic complex [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(4-MePy)2] (11) is obtained by treating the starting dimer 3 with TlBF4 and 4-MePy. The addition of Ph2PCH2CH2PPh2 (dppe) to the starting dimer 3 leads to [{Pd2[CH2SiPh2(CH2NC5H10)-κ²C,N]2Cl2}(μ-dppe)] (13) or to [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(dppe)]Cl (11), depending on the stoichiometry. NMR data reveal that the Pd−N bond in 11 is transiently opened in solution. [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(dppe)]BF4 (14) is obtained from the latter compound upon treatment with TlBF4. The chelate complexes [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(acac)] (16) (acac = acetylacetonate) and [Pd{CH2SiPh2(CH2NC5H10)-κ²C,N}(S2CNEt2)] (15) are obtained by reaction of the starting chloro-bridged dimer 3 with Tl(acac) and NaS2CNEt2, respectively. The solid state structures of palladacycles 3, 4, 8, 9, 10, and 15 were determined by X-ray diffraction methods.

The reactions of chlorobridged cyclometalated complexes [Pd(C−N)(μ-Cl)]2 (C−N = orthometalated N,N-dimethylbenzylamine, dmba; 2-(para-tolyl)pyridine, p-tolpy; azobenzene, azb; N,N-dimethyl-1-naphthylamine, dmna; and 2-benzylpyridine, bzpy) with Li(Fmes) (Fmes = 2,4,6-tris(trifluoromethyl)phenyl or nonafluoromesityl) give, after hydrolysis, neutral aquo complexes [Pd(C−N)(Fmes)(OH2)], where the ipso carbon atoms of the Fmes and the cyclometalated ligand are coordinated cis, as shown by an X-ray diffraction study of [Pd(dmba)(Fmes)(OH2)]. The aquo ligand is readily displaced by other ligands, giving complexes [Pd(C−N)(Fmes)L] (L = PPh3, 2,6-lutidine, NH3, CN^tBu, CO) when monodentate ligands are employed or [Pd(dmba-C)(Fmes)(2,2‘-bipy)], which contains a chelating 2,2‘-bipyridyl and a monodentate C-bonded dmba. Different processes in solution are detected for the complexes containing the bulkier ligands:  ligand rotation in the complex with PPh3; inversion of the bipy ligand in [Pd(dmba-C)(Fmes)(2,2‘-bipy)]; and equilibria with residual water in the solutions of [Pd(C−N)(Fmes)(lut)] and [Pd(dmba-C)(Fmes)(2,2‘-bipy)].

The complex [Au(Fmes)(tht)] (Fmes = 2,4,6-tris(trifluoromethyl)phenyl or nonafluoromesityl; tht = tetrahydrothiophene) was obtained by reaction of [AuCl(tht)] and Li(Fmes). Monoarylated complexes are readily obtained when the tht ligand is displaced by other neutral ligands, giving [Au(Fmes)L] (L = PPh3, P(o-tol)3, 2,6-lutidine) or [Au2(Fmes)2(μ-bipy)] (bipy = 2,2‘-bipyridyl), the latter containing a bridging bipy ligand. tht can also be displaced by halides to give the gold anionic complexes NBu4[Au(Fmes)X] (X = Cl, Br, I). [Au(Fmes)(NCMe)] is obtained from the latter by treatment with TlBF4 in the presence of MeCN. The bis-arylated complexes NR4[Au(Fmes)2] (R = Et, Bu) were obtained by treatment of NR4[AuBr2] with excess Li(Fmes). They react with AgBF4 and 4-methylpyridine to give [Ag(4-Mepy)2][Au(Fmes)2]. Oxidative addition of halogens to the monoarylated NBu4[Au(Fmes)X] and the bis-arylated NR4[Au(Fmes)2] gives the gold(III) complexes NBu4[Au(Fmes)X3] and NR4[trans-Au(Fmes)2X2], respectively. The structures of the bis-arylated gold(I) and -(III) complexes NBu4[Au(Fmes)2] and NEt4[trans-Au(Fmes)2I2] were determined by X-ray diffraction. An analysis of nonbonded distances and torsion angles suggests that steric repulsion of neighboring CF3 groups is reduced by mutual rotation of the Fmes rings in the former complex but by rotation of the CF3 groups themselves in the latter (in which the Fmes rings are exactly coplanar).

Decarbonylation of the dimolybdenum complexes [Mo2(η⁵-C5H4R)2(CO)4(μ-dppm)] (R = H, Me, dppm = Ph2PCH2PPh2) occurs readily upon heating in tetrahydrofuran or toluene solution to afford with good yield the phosphido complexes [Mo2(η⁵-C5H4R)2(μ-CH2PPh2)(μ-PPh2)(CO)2], which arise from an irreversible P−C(sp³) bond cleavage in the backbone of the dppm ligand. Other minor products in these reactions are the oxo complexes [Mo2(η⁵-C5H4R)2(μ-CH2PPh2)(O)(μ-PPh2)(CO)], which are formed by the action of oxygen on the former dicarbonyl compounds, and the triply-bonded complexes [Mo2(η⁵-C5H4R)2(CO)2(μ-dppm)], in which the dppm ligand remains intact. By contrast, photochemical decarbonylation of the parent tetracarbonyl complexes at 10 °C yields the triply-bonded dicarbonyls as major products, along with a small amount of the monocarbonyl complexes [Mo2(η⁵-C5H4R)2(μ-CH2PPh2)(μ-PPh2)(μ-CO)]. Separate experiments show that the latter compounds are formed from [Mo2(η⁵-C5H4R)2(μ-CH2PPh2)(μ-PPh2)(CO)2] under photolytic conditions, this reaction being reversible. Thus it is concluded that the P−C(sp³) cleavage of the dppm ligand is fairly well suppressed at ambient temperatures or below. The reactions of all the above unsaturated species with CN^tBu proceed rapidly at room temperature. In this way, the new isocyanide derivatives [Mo2(η⁵-C5H4Me)2(μ-CH2PPh2)(μ-PPh2)(CN^tBu)(μ-CO)(CO)], [Mo2(η⁵-C5H5)2(μ-CH2PPh2)(μ-PPh2)(CN^tBu)(CO)], and [Mo2(η⁵-C5H4R)2(μ-η¹,η²-CN^tBu)(CO)2(μ-dppm)] have been prepared. All of them are formed in good yields as single isomers but have a rather low stability. Reaction of the monocarbonyl derivative with atmospheric oxygen gives the oxo complex [Mo2(η⁵-C5H5)2(μ-CH2PPh2)(μ-O)(μ-OPPh2)(CN^tBu)(CO)], which is also obtained as a single isomer. In marked contrast to their ditungsten analogues, the isocyanide-bridged compounds [Mo2(η⁵-C5H4R)2(μ-η¹,η²-CN^tBu)(CO)2(μ-dppm)] do not experience C−H bond cleavages in their cyclopentadienylic rings to a significant extent.

Complexes containing one or two Fmes ligands (Fmes = 2,4,6-tris(trifluoromethyl)phenyl = nonafluoromesityl) either trans or cis are obtained by treating palladium(II) chloro complexes with Li(Fmes):  trans-[PdCl2L2] (L = tetrahydrothiophene (tht), PPh3) lead to trans-[Pd(Fmes)ClL2] (L = tht, PPh3) or trans-[Pd(Fmes)2L2] (L = tht); [PdCl2(L-L)] (L-L = 1,5-cyclooctadiene, 2,2‘-bipyridine) give [Pd(Fmes)Cl(L-L)] (L-L = COD, bipy) or [Pd(Fmes)2(bipy)]. The structures of two complexes containing two Fmes ligands in trans and cis arrangement, trans-[Pd(Fmes)2(tht)2] (2) and [Pd(Fmes)2(bipy)] (6), respectively, have been determined by X-ray diffraction. In spite of the severe steric congestion the complexes are four coordinated. Distortions due to the bulkiness of the ortho substituents and short Pd···F3C-ortho distances are observed. The high degree of steric crowding is also responsible for slow rotation around the Pd−P bonds in the complex trans-[Pd(Fmes)Cl(PPh3)2]. ΔG^&thermod; associated with this motion is 12.8 kcal mol^-1, one of the highest values reported so far for rotation around M−PPh3 bonds. Complexes 2 and 6 are redox inactive by cyclic voltammetry in the range −1.8 to +1.8 V.