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A theoretical analysis of two aspects of the mechanism of reductive elimination is presented—how the choice of central metal and peripheral ligands affects the activation energy for reductive elimination from a four-coordinate MR2(PR3)2 complex and how ligand asymmetry controls cis-trans rearrangements and elimination pathways proceeding through three-coordinate intermediates. The following conclusions emerge: (1) In the four-coordinate complex, the better the σ-donating capability of the leaving groups, the more facile the elimination; (2) Stronger donor ligands trans to the leaving groups will increase the barrier to elimination; (3) The reductive elimination barrier in four-coordinate complexes is controlled by the energy of an antisymmetric b2 orbital, which in turn depends on the energy of the metal levels. The activation energy for such direct reductive elimination should be, and is, substantially lower for Ni than for Pt or Pd; (4) T-shaped trans PdLR2, arising from dissociation of L in PdL2R2, will encounter a substantial barrier to polytopal rearrangement to cis PdLR2, which in turn has an open channel for reductive elimination of R2; (5) If the leaving groups are poor donors, cis-trans isomerization in the three-coordinate manifold should be easier than elimination.

The hydrothermal reaction of YbCl(3) small middle dot6H(2)O with 1,2,4,5-benzenetetracarboxylic dianhydride resulted in [[Yb((b)btec)(1/4)((d)btec)(3/6)(H(2)O)(2)](4).6H(2)O](n)() (1) (H(4)btec = 1,2,4,5-benzenetetracarboxylic acid), and the solvothermal reaction of Er(NO(3))(3) small middle dot6H(2)O or TbCl(3).6H(2)O with 1,2,4,5-benzenetetracarboxylic dianhydride in H(2)O/acetic acid gave rise to [[Er(2)((c)btec)(2/4)((e)btec)(2/4)((f)btec)(2/4)(H(2)O)(4)].4H(2)O](n)() (2) and [[Tb(H(2)btec)(2/4)((f)btec)(3/6)(H(2)O)].2H(2)O](n)() (3), respectively. Complex 1 crystallizes in monoclinic space group C2/m with a = 20.8119(5) A, b = 17.6174(1) A, c = 5.7252(2) A, beta = 92.324(1) degrees, and Z = 1. 1 possesses a three-dimensional framework consisting of eight-coordinate ytterbium centers and two kinds of channels along the c axis. Complex 2 crystallizes in triclinic space group P with a = 9.6739(5) A, b = 11.0039(5) A, c = 11.5523 A, alpha = 104.8330(10) degrees, beta = 91.0000(10) degrees, gamma = 114.2570(10) degrees, and Z = 2. 2 has a three-dimensional framework comprising both eight- and nine-coordinate erbium centers and channels along the a axis. Complex 3 crystallizes in monoclinic space group P2(1)/n with a = 10.7246(12) A, b = 7.1693(9) A, c = 17.158(2) A, beta = 97.109(2) degrees, and Z = 4. 3 shows a three-dimensional framework containing nine-coordinate terbium centers and channels along the b axis. Uncoordinated water molecules occupy the channels in the three complexes. TGA and XRPD were determined for the three complexes, and the results illustrate that the framework of 1 is retained upon removal of uncoordinated and coordinated water molecules.

A series of mononuclear thio complexes of pentamethylcyclopentadienyl−molybdenum(VI) and −tungsten(VI) have been synthesized via C−S bond-cleaving reactions of thiolates. Use of Li2S2 for sulfurization of Cp*MoCl4 resulted in the known dinuclear complex, anti-Cp*2Mo2(S)2(μ-S)2 (1), while the analogous reaction of Cp*WCl4 gave rise to anti-Cp*2W2(S)2(μ-S)2 (2) and (PPh4)[Cp*W(S)3] (3), the latter of which was isolated after the subsequent cation exchange reaction with PPh4Br. In contrast, the reaction of Cp*WCl4 with Li2edt (edt = SCH2CH2S) followed by treatment with PPh4Br generated 3 as the sole isolable product in high yield. A similar reaction between Cp*WCl4 and LiStBu afforded Cp*W(S)2(StBu) (6), which turned out to be thermally unstable in solution and gradually degraded to 2. In these reactions of Cp*WCl4 with lithium thiolates, a facile C−S bond cleavage took place and the tungsten atom was oxidized from W(V) to W(VI). On the other hand, the Mo(IV) thiolate complexes, Cp*Mo(StBu)3 (4) and (PPh4)[Cp*Mo(edt)2] (5), were formed from the Cp*MoCl4/LiStBu and Cp*MoCl4/Li2edt/PPh4Br reaction systems. The complex 4 was readily oxidized by dry O2 producing Cp*Mo(O)2(StBu) (7) exclusively, while the reactions of 4 with NH2NMe2 and NH2NHPh occurred slowly to yield Cp*Mo(S)2(StBu) (8). The hydrazines acted as oxidants, presumably by cleaving the N−N bond, and promoted the C−S bond rupture of tert-butyl thiolate and concomitant oxidation of molybdenum from Mo(IV) to Mo(VI). Elemental sulfur S8 and grey selenium also acted as oxidants in the reactions with 4, leading to a complex mixture of products. From the 4 + S8 reaction, the complexes 1, 8, and Cp*Mo(O)(S)(StBu) (9) were produced, and the 4 + Se reaction lead to 8 and anti-Cp*2Mo2(E)2(μ-E)2 (10; E = S, Se). Finally treatment of 8 with Li2S2 and PPh4Br afforded (PPh4)[Cp*Mo(S)3] (11). We found that 11 was synthesized more easily by a one-pot reaction of 4, 1/4 equiv of S8, and Li2S2 in THF. The trithio complexes, 3 and 11, reacted very cleanly with PhC⋮CPh generating (PPh4)[Cp*M(S)(S2C2Ph2)] (M = W (12), Mo (13)), respectively. A kinetic study of these reactions showed that they were first order in PhC⋮CPh and first order in 3 or 11 with appreciable negative entropies of activation and that the activation barrier was higher for the molybdenum reaction. The crystal structures of 3−8 and 11−13 were determined by the X-ray analysis.

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Merging cooperative Si-H bond activation and electrophilic aromatic substitution paves the way for C-3-selective indole C-H functionalization under electronic and not conventional steric control. The Si-H bond is heterolytically split by the Ru-S bond of a coordinatively unsaturated cationic ruthenium(II) complex, forming a sulfur-stabilized silicon electrophile. The Wheland intermediate of the subsequent Friedel-Crafts-type process is assumed to be deprotonated by the sulfur atom, no added base required. The overall catalysis proceeds without solvent at low temperature, only liberating dihydrogen.

Coordinatively unsaturated ruthenium complexes with a tethered SDmp (Dmp=2,6-dimesitylphenyl) ligand, [(DmpS)Ru(PR(3))][BAr(F) (4)] (3 a: R=Et; 3 b: R=Ph; Ar(F)=3,5-(CF(3))(2)C(6)H(3)), were synthesized by the reactions of [{(p-cymene)RuCl}(2)(mu-Cl)(2)], LiSDmp, phosphines, and NaBAr(F) (4). The Ru--S bonds in 3 a and 3 b were found to serve as the polarized reactive site in reactions with alkyl halides, diazoalkanes, (p-tosyliminoiodo)benzene, phenylacetylene, and H(2). Alkylation of 3 a and 3 b with methyl iodide or ethyl bromide occurred instantaneously to give the thioether complexes [(DmpSR')RuX(PR(3))][BAr(F) (4)] (4 a: R=Et, R'=Me, X=I; 4 b: R=R'=Et, X=Br; 4 c: R=Ph, R'=Me, X=I; 4 d: R=Ph, R'=Et, X=Br). Treatment of 3 a with diazoalkanes N(2)CHR (R=CO(2)Et, SiMe(3)) led to the cycloaddition of carbenes to the Ru--S bond to form [DmpS(CHR)Ru(PEt(3))][BAr(F) (4)] (5 a: R=CO(2)Et; 5 b: R=SiMe(3)), whereas the reaction with (p-tosyliminoiodo)benzene gave rise to [DmpS{NS(O)(C(6)H(4)-4-CH(3))O}Ru(PEt(3))][BAr(F) (4)] (6), which contains a five-membered ruthenacycle of RuSNSO. Addition of phenylacetylene to the Ru--S bond occurred reversibly to produce the vinyl sulfide complexes [DmpS(PhCCH)Ru(PR(3))][BAr(F) (4)] (7 a: R=Et; 7 b: R=Ph). On the other hand, the phenylacetylene at ruthenium slowly isomerized to vinylidene and bridged Ru and S in the products, [DmpS{C(CHPh)}Ru(PR(3))][BAr(F) (4)] (8 a: R=Et; 8 b: R=Ph). Complex 3 a catalyzed the hydrogenation of acetophenone, in which the heterolytic H-H splitting at the Ru-S site is suggested to be involved in the mechanism.

Half-sandwich iron complexes of N-heterocyclic carbenes, Cp*Fe(L(R))Cl (2a; L(Mes) = 1,3-dimesityl-imidazol-2-ylidene, 2b; L(iPr) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, Cp* = eta(5)-C5Me5), have been synthesized by the reaction of Cp*Fe{N(SiMe3)2} (1) with the corresponding imidazolium salts. Treatment of 2a with either methyllithium or phenyllithium replaces the chloride with either a methyl or a phenyl group, generating Cp*Fe(L(Mes))R (3a; R = Me, 3b; R = Ph). These complexes, in turn, undergo cyclometalation at elevated temperatures, and Cp*Fe{kappa2-(C,C)-L'(Mes)} (4; L'(Mes) = CH2C6H2-3,5-Me2-2-(3-mesityl-imidazol-2-ylidene-1-yl)) was isolated. On the other hand, methylation of 2b at room temperature leads directly to the formation of a cyclometalated complex, Cp*Fe{kappa2-(C,C)-L'(iPr)} (6; L'(iPr) = CH2CH(CH3)(3-isopropyl-4,5-dimethylimidazol-2-ylidene-1-yl)). The Fe(II) center of 6 traps atmospheric dinitrogen reversibly to produce a dinuclear end-on N2 complex [Cp*Fe{kappa2-(C,C)-L'(iPr)}]2(mu-eta(1):eta(1)-N2) (7). Complex 6 also promotes C-H bond activation of thiophene, furan, benzothiophene, and benzofuran at room temperature. In these reactions, C-H bond cleavage occurred exclusively at the 2-position of the rings, generating Cp*Fe(L(iPr))(2-C4H3E) (8; E = S, 9; E = O) and Cp*Fe(L(iPr))(2-C8H5E) (10; E = S, 11; E = O), while C-H cleavage took place mainly at the 4-position in the case of pyridine. Coupling reactions between heteroarenes and catecholborane (HBcat) can be carried out by treatment of 6 with heteroarenes followed by the addition of excess HBcat, giving rise to 2-boryl-heteroarenes and the borohydride complex Cp*Fe(L(iPr))(H2Bcat) (14).