Transition Metal Complexes Containing All-Carbon Ligands

All-Inorganic sp-Chain Ligands: Isoelectronic B/N Analogues of E. O. Fischer's Alkynylcarbynes

Borylation of a tungsten-bound N2 ligand and halide abstraction provides access to a cationic complex with an unprecedented linear NNBR ligand. This complex undergoes [3+2] cycloaddition with azides, and an unexpected chain-extension reaction with an iminoborane, leading to a complex with a five-atom B/N chain. These two [NNBR]-containing complexes, inorganic analogues of E. O. Fischer's alkynylcarbynes, are very rare examples of molecules containing all-inorganic chains of sp-hybridized atoms.

Syntheses and Structures of trans-bis(Alkenylacetylide) Ruthenium Complexes

A series of ruthenium alkenylacetylide complexes trans-[Ru{C≡CC(=CH₂ )R}Cl(dppe)₂ ] (R=Ph (1 a), ^c C₄ H₃ S (1 b), 4-MeS-C₆ H₄ (1 c), 3,3-dimethyl-2,3-dihydrobenzo[b]thiophene (DMBT) (1 d)) or trans-[Ru{C≡C-^c C₆ H₉ }Cl(dppe)₂ ] (1 e) were allowed to react with the corresponding propargylic alcohol HC≡CC(Me)R(OH) (R=Ph (A), ^c C₄ H₃ S (B), 4-MeS-C₆ H₄ (C), DMBT (D) or HC≡C-^c C₆ H₁₀ (OH) (E) in the presence of TlBF₄ and DBU to presumably give alkenylacetylide/allenylidene intermediates trans-[Ru{C≡CC(=CH₂ )R}{C=C=C(Me)}(dppe)₂ ]PF₆ ([2]PF₆ ). These complexes were not isolated but deprotonated to give the isolable bis(alkenylacetylide) complexes trans-[Ru{C≡CC(=CH₂ )R}₂ (dppe)₂ ] (R=Ph (3 a), ^c C₄ H₃ S (3 b), 4-MeS-C₆ H₄ (3 c), DMBT (3 d)) and trans-[Ru{C≡C-^c C₆ H₉ }₂ (dppe)₂ ] (3 e). Analogous reactions of trans-[Ru(CH₃ )₂ (dmpe)₂ ], featuring the more electron-donating 1,2-bis(dimethylphosphino)ethane (dmpe) ancillary ligands, with the propargylic alcohols A or C and NH₄ PF₆ in methanol allowed isolation of the intermediate mixed alkenylacetylide/allenylidene complexes trans-[Ru{C≡CC(=CH₂ )R}{C=C=C(Me)}(dmpe)₂ ]PF₆ (R=Ph ([4 a]PF₆ ), 4-MeS-C₆ H₄ ([4 c]PF₆ ). Deprotonation of [4 a]PF₆ or [4 c]PF₆ gave the symmetric bis(alkenylacetylide) complexes trans-[Ru{C≡CC(=CH₂ )R}₂ (dmpe)₂ ] (R=Ph (5 a), 4-MeS-C₆ H₄ (5 c)), the first of their kind containing the dmpe ancillary ligand sphere. Attempts to isolate bis(allenylidene) complexes [Ru{C=C=C(Me)R}₂ (PP)₂ ]²⁺ (PP=dppe, dmpe) from treatment of the bis(alkenylacetylide) species 3 or 5 with HBF₄  ⋅ Et₂ O were ultimately unsuccessful.

A unique series of chromium(iii) mono-alkynyl complexes supported by tetraazamacrocycles

Described herein is the synthesis and characterization of macrocyclic Cr^III mono-alkynyl complexes. By using the meso-form of the tetraazamacrocycle HMC (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), trans-[Cr(HMC)(C₂Ph)Cl]OTf (1a), trans-[Cr(HMC)(C₂Np)Cl]OTf (2a), trans-[Cr(HMC)(C₂C₆H₄^tBu)Cl]OTf (3a), and trans-[Cr(HMC)(C₂(3,5-Cl₂C₆H₃))Cl]OTf (4a) complexes have been realized. These complexes were synthesized in high yield through the reaction of trans-[Cr(meso-HMC)(C₂Ar)₂]OTf (1b-4b) with stoichiometric amounts of methanolic HCl. Single crystal X-ray diffraction showed that the trans-stereochemistry and pseudo-octahedral geometry is retained in the desired mono-alkynyl complexes. The absorption spectra of complexes 1a-4a display d-d bands with distinct vibronic progressions that are slightly red shifted from trans-[Cr(HMC)(C₂Ar)₂]⁺ with approximately halved molar extinction coefficients. Time-delayed measurements of the emission spectra for complexes 1a-4a at 77 K revealed phosphorescence with lifetimes ranging between 343 μs (4a) and 397 μs (1a). The phosphorescence spectra of 1a-4a also exhibit more structuring than the bis-alkynyl complexes due to a strengthened vibronic coupling between the Cr^III metal center and alkynyl ligands.

Mix and (Mis)match: further studies of the electronic structure and mixed-valence characteristics of 1,4-diethynylbenzene-bridged bimetallic complexes

The 1,4-diethynylbenzene motif is commonly employed as a bridging ligand in bimetallic molecular systems intended to show pronounced intramolecular electronic interactions, delocalized electronic structures and 'wire-like' properties between the metal fragments at the ligand termini. In contrast to these expectations, the donor-acceptor compounds [{Cp'(CO)xM'}(μ-C[triple bond, length as m-dash]CC6H4C[triple bond, length as m-dash]C){M(PP)Cp'}]n+ [n = 0, 1; M'(CO)xCp' = Fe(CO)2Cp, W(CO)3Cp*; M(PP)Cp' = Fe(dppe)Cp, Fe(dppe)Cp*, Ru(PPh3)2Cp, Ru(dppe)Cp, Ru(dppe)Cp*] display remarkably little bridge-mediated electronic interaction between the electron-rich {M(PP)Cp'} and electron-poor {M'(CO)xCp'} fragments in the ground state. However, a relatively high-energy (26 000-30 000 cm-1) M-to-M' charge transfer can be identified. One-electron oxidation is largely localized on the {M(C[triple bond, length as m-dash]CR)(PP)Cp'} fragment and gives rise to a new charge transfer band with bridging-ligand-to-{M(PP)Cp'}+ (M'(CO)xCp' = Fe(CO)2Cp) or M'-to-M(+) (M(CO)xCp' = W(CO)3Cp*) character. The localized electronic ground state of these complexes is better revealed through analysis of the IR spectra, taking advantage of the well-resolved ν(C[triple bond, length as m-dash]C) and ν(CO) bands and IR spectroelectrochemical methods, than through the more classical analysis based on the concepts of Marcus-Hush theory and analysis of the putative IVCT electronic transition. The conclusions are supported by DFT calculations using the BLYP35 functional.

An Ru-Substituted Tris(ethynyl)methyl Cation: Synthesis, Properties, and Structure of [{Cp(dppe)Ru(C≡C)}3C]PF6·C6H6

The dark blue complex [{Cp(dppe)Ru(C≡C)}3C]PF6 1 (Cp=cyclopentadienyl, dppe=1,2-bis(diphenylphosphino)ethane) was obtained in 46% yield by treatment of Ru(C≡CH)(dppe)Cp with CuCl/TMEDA (tetramethylethanediamine), followed by KOH and [NH4]PF6 in acetone; it was accompanied by known complexes {Cp(dppe)Ru}C≡CC≡C{Ru(dppe)Cp} 2 (22%) and yellow [1,3-{Cp(dppe)Ru}2C4H3]PF6 3 (2.6%). The structure of the cationic fragment of 1 in its benzene solvate consists of a central planar C attached to three C≡CRu(dppe)Cp fragments. The cation of 3 consists of a cyclobuten-1,3-diyl group bearing two Ru(dppe)Cp groups. The 13C NMR resonance of the central C in 1 is found at δ 66.11. The cyclic voltammogram of 1 contains three irreversible oxidation waves at +0.87, +0.79, and +0.25V, together with a reversible reduction wave at −1.38V (versus FeCp2/[FeCp2]+).

Hydrogenating an organometallic carbon chain: buten-yn-diyl (CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C) as a missing link

The sequential reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [Ru(CO)2(PPh3)3], and N-chlorosuccinimide affords the binuclear tetracarbido complex [Ru2(μ-C[triple bond, length as m-dash]CC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4]. This may be compared with the first example of a butenyndiyl bridged bimetallic complex [Ru2(μ-CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4] which is obtained from the reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [RuHCl(CO)(PPh3)3] followed by carbonylation. Characterisational data are discussed with reference to constituent model complexes [Ru(C[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] and [Ru(CH[double bond, length as m-dash]CH2)Cl(CO)2(PPh3)2] in addition to DFT analysis of the bonding in the complexes [Ru2(μ-L)Cl2(CO)4(PMe3)4] (L = C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CH-CH[double bond, length as m-dash]CH). A range of other tetracarbido complexes which may be prepared from [RuCl(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)(CO)2(PPh3)2] is also described and includes [RuAu(μ-C4)Cl(CO)3(PPh3)3], [RuIr(μ-C4)Cl(CO)3(PPh3)4], [RuIr(μ-C4)H(NCMe)(CO)3(PPh3)4]BF4, [RuIr(μ-C4)Cl(η2-O2)(CO)3(PPh3)4], [Ru2Hg(μ-C4)2Cl2(CO)4(PPh3)4], [Ru2Pt(μ-C4)2Cl2(CO)4(PPh3)6] and [Ru2(μ-C4)HCl(CO)4(PPh3)4].

Wire like diplatinum, triplatinum, and tetraplatinum complexes featuring X[PtCCCCCCCC]mPtX segments; iterative syntheses and functionalization for measurements of single molecule properties

The title complexes are accessed from platinum chloride and Z(CC)₂SiMe₃ (Z = Me₃Sn, H) building blocks via oxidative homocouplings and cross couplings.

Through-conjugation of two phosphaalkyne (‘CP’) moieties mediated by a bimetallic scaffold

The bis-cyaphide complex [{Ru(dppe)₂}₂{μ-(CC)₂C₆H₄-p}(CP)₂] is the first molecule to incorporate two phosphaalkyne ‘CP’ moieties within a through-conjugated scaffold, and demonstrates interesting redox behaviour.

Optimised Syntheses of the Half-Sandwich Complexes FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp

Thanks to their synthetic versatility, the half-sandwich metal chlorides MCl(dppe)(η5-C5R5) [M = Fe, Ru; dppe = 1,2-bis(diphenylphosphino)ethane, R = H (cyclopentadiene, Cp), CH3 (pentamethylcyclopentadiene, Cp*)] are staple starting materials in many organometallic laboratories. Here we present an overview of the synthetic methods currently available for FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp, and describe in detail updated and optimised multigram syntheses of all four compounds.