We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-CH=CH-R where the phosphine ligands at the (PR'3)2Ru(CO)Cl={Ru} moiety, the coordination number at the metal (L = 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R = nbutyl, phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh3)2(eta1:eta2-nBuHC=CHCCnBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule of 1-hexyne, of the hexenyl complexes (nBuCH=CH)Ru(CO)Cl(PiPr3)2 (1c) and (nBuCH=CH)Ru(CO)Cl(PPh3)2(NC5H4COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CH=CH)Ru(CO)Cl(PiPr3)2 (3c) and (1-Pyr-CH=CH)Ru(CO)Cl(PPh3)3 (3a-P) have been established by X-ray crystallography. All vinyl complexes undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as pi-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are significantly smaller than is expected of a metal-centered oxidation process and are further diminished as the vinyl CH=CH entity is incorporated into a more extended pi-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the average g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation processes. This renders them a class of truly "non-innocent" ligands in organometallic ruthenium chemistry. Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes from nbutyl to 1-pyrenyl.

The use of the terphenyl substituent -C(6)H(3)-2,6-Mes(2) (abbreviated Ar) has permitted the synthesis of several new low-coordinate beryllium compounds. Reaction of 1 equiv of LiAr with BeCl(2)(OEt(2))(2) or BeBr(2)(OEt(2))(2) (1) gives the monomeric complexes ArBeX(OEt(2)) (X = Cl (2); Br (3) featuring three-coordinate berylliums. Treatment of 2 with 1 equiv of LiSMes (Mes = -C(6)H(2)-2,4,6-t-Bu(3)) affords the three-coordinate thiolate derivative ArBeSMes(OEt(2)) (4). The reaction of 2 with LiNHPh, LiNHSiPh(3), or LiN(SiMe(3))(2) affords the unstable dimer (ArBeNHPh)(2) (5) or the monomers ArBeNHSiPh(3)(OEt(2)) (6) and ArBeN(SiMe(3))(2) (7). The last is the first example of a two-coordinate beryllium center in the solid state. The addition of 1 equiv of 2 to NaMo(eta(5)-C(5)H(5))(CO)(3) gives the isocarbonyl complex Ar(THF)(2)Be(OC)(3)Mo(eta(5)-C(5)H(5)) (8), which features four-coordinate beryllium bound to Ar, two THF ligands, and an oxygen from one of the molybdenum-bound carbonyls. Reaction of 2 with a 1:1 mixture of LiN(SiMe(3))(2) and PhCN affords the six-membered-ring compound PhC(NSiMe(3))(2)(BeCl)(2)N(SiMe(3))(2) (9) and the four-coordinate monomer Be{(NSiMe(3))(2)CPh}(2) (10). Compounds 1-10 were characterized by X-ray crystallography, and 1 and 4 and 6-10 were also characterized by (1)H, (9)Be, and (13)C NMR spectroscopy. X-ray data at 130 K (1-9) or 185 K (10) with Mo Kalpha (lambda = 0.710 73 Å) (1, 2a, 3, 7, 8) or Cu Kalpha (lambda = 1.541 78 Å) (2b, 4-6, 9, 10). BeBr(2)(OEt(2))(2) (1), a = 11.690(5) Å, b = 10.191(3) Å, c = 12.131(5) Å, beta = 114.67(3) degrees, V = 1313.3(9) Å(3), space group P2(1)/n, Z = 4, R(1) = 0.062; ArBeCl(OEt(2)) (2a), a = 13.136(3) Å, b = 13.877(3) Å, c = 28.092(6) Å, V = 5121(2) Å(3), space group Pbca, Z = 8, R(1) = 0.058; ArBeCl(OEt(2)) (2b), a = 8.857(1) Å, b = 8.8977(9) Å, c = 18.198(7) Å, alpha = 86.437(8) degrees, beta = 82.677(8) degrees, gamma = 62.405(7) degrees, V = 1260.5(2) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.048; ArBeBr(OEt(2)) (3), a = 8.873(5) Å, b = 8.847(5) Å, c = 18.251(7) Å, alpha = 86.54(4) degrees, beta = 83.17(4) degrees, gamma = 64.14(4) degrees, V = 1280(1) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.071; ArBeSMes(OEt(2)).0.5C(6)H(14) (4.0.5C(6)H(14)), a = 9.732(1) Å, b = 11.190(1) Å, c = 21.841(2) Å, alpha = 75.225(7) degrees, beta = 81.137(8) degrees, gamma = 73.382(8) degrees, V = 2195.3(4) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.062; (ArBeNHPh)(2).C(4)H(10)O (5.C(4)H(10)O), a = 11.894(2) Å, b = 12.212(2) Å, c = 18.709(3) Å, beta = 99.24(1) degrees, V = 2682.4(7) Å(3), space group P2(1), Z = 2, R(1) = 0.045; ArBeNHSiPh(3)(OEt(2)) (6), a = 11.959(2) Å, b = 16.655(2) Å, c = 19.718(2) Å, beta = 105.368(9) degrees, V = 3786.9(8) Å(3), space group P2(1)/c, Z = 4, R(1) = 0.047; ArBeN(SiMe(3))(2) (7), a = 12.623(3) Å, b = 15.404(4) Å, c = 15.502(3) Å, V = 3014(1) Å(3), space group Pbcn, Z = 4, R(1) = 0.046; Ar(THF)(2)Be(OC)(3)Mo(eta(5)-C(5)H(5)).2C(7)H(8) (8.2C(7)H(8)), a = 19.111(4) Å, b = 11.976(3) Å, b = 21.241(5) Å, beta = 103.47...

In the last decade a major theme of organometallic chemistry has been the design and development of alternative ligand systems capable of stabilizing monomeric metal complexes while provoking novel reactivity. Exploration of this field is driven by the potential use of these complexes in catalysis and organic synthesis. Examples of monoanionic chelating Ndonor ligands that have received much recent attention (Scheme 1) include the b-diketiminate (I) [1] and the amidinate (II) [2] ligand systems. Much less attention has been given to the closely related triazenides (III). [3, 4] This may be attributed to the lack of suitable ligands that are sterically crowded enough to prevent undesirable ligand redistribution reactions and allow better control of the electronic and steric properties at the metal center.Triazenides are weaker donors than the isoelectronic amidinates and the related b-diketiminates, and should induce greater electrophilicity at a bonded metal atom. [5] This is reflected by the results of an NBO (natural bond orbitals) analysis of the energy-minimized structures [6] of the model anions 1,3-diphenyl-1,3-diketiminate (I M ), 1,3-diphenyl-1,3-diazaallyl (II M ), and 1,3-diphenyltriazenide (III M ) (see Supporting Information), which shows an NPA (natural population analysis) charge for the chelating N atoms of À0.54, À0.60, and À0.38, respectively.We recently succeeded in the preparation of aryl-substituted, sterically crowded triazenes. Ligands of this type may be synthesized in excellent yields by the reaction of different substituted 2-lithiobiphenyls with the m-terphenyl azide 1, followed by hydrolysis (Scheme 2).In a first attempt to test their properties, we have used the obtained triazenes to stabilize pentafluorophenyl compounds of the heavier alkaline-earth metals calcium, strontium, and barium. The heteroleptic pentafluorophenyl triazenides are accessible in tetrahydrofuran as solvent by a convenient onepot transmetalation/deprotonation [7] reaction from the triazene 2 a (HN 3 ArAr'), bis(pentafluorophenyl)mercury, and the corresponding alkaline-earth metal (Scheme 3). After crystallization from n-heptane, either the THF-free compounds [M(C 6 F 5 )(N 3 ArAr')] (M = Sr (4), Ba (5)) or the solvate [Ca(C 6 F 5 )(N 3 ArAr')(thf)] (3) were isolated in good yields. It is remarkable that attempts to replace the pentafluorophenyl substituents by a second triazenide ligand have not been successful so far. Apparently, the steric bulk of the latter prevents further substitution or ligand redistribution and therefore formation of the homoleptic complexes. [8] Solutions of 4 or 5 in aromatic or aliphatic solvents show considerable thermal stability and can be stored at ambient