Magnesium(II) complexes of 2,4-N,N'-disubstituted 1,3,5-triazapentadienyl ligands: synthesis and characterization of [N(Dipp)C(NMe2)NC(NMe(2))N(SiMe3)MgBr]2 and [N(R)C(R')NC(R')N(SiMe3)]2Mg (Dipp = 2,6-iPr2-C6H3, R = Ph, SiMe(3); R' = NMe2, 1-piperidino)

Treatment of the appropriate lithium or sodium 2,4-N,N'-disubstituted 1,3,5-triazapentadienate [RNC(R')NC(R')N(SiMe(3))M](2) (R = Ph, 2,6-(i)Pr(2)-C(6)H(3)(Dipp) or SiMe(3); R' = NMe(2) or 1-piperidino; M = Li or Na) with one or half equivalent portion of MgBr(2)(THF)(2) in Et(2)O under mild conditions furnishes in good yield the first structurally characterized molecular magnesium 2,4-N,N'-disubstituted 1,3,5-triazapentadienates [DippNC(NMe(2))NC(NMe(2))N(SiMe(3))MgBr](2) (1), [{RNC(R')NC(R')N(SiMe(3))}(2)Mg] (R = Ph, R' = NMe(2) 2; R = Ph, R' = 1-piperidino 3; R = SiMe(3), R' = 1-piperidino 4). The solid-state structure of 1 is dimeric and those of 2, 3, and 4 are monomeric. The ligand backbone NCNCN in 1 adopts a W-shaped configuration, while in 2, 3 and 4 adopts a U-shaped configuration.     

Aggregation of [(tBu3SiS)MX]: structures of {[Br2Fe(mu-SSitBu3)2)FeBr(THF)]Na(THF)4}infinity, cis-[(THF)FeI]2(mu-SSitBu3)2, [(tBu3SiS)Fe]2(mu-SSitBu3)2, and comparative structure and magnetism studies of [(tBu3SiS)MX]n (M = Fe, Co, X = Cl, n = 12; M = Fe, Ni, X = Br, n = 12; M = Fe, X = I, n = 14)

A convenient synthesis of (t)Bu(3)SiSH and (t)Bu(3)SiSNa(THF)(x)() led to the exploration of "(t)Bu(3)SiSMX" aggregation. The dimer, [((t)Bu(3)SiS)Fe](2)(mu-SSi(t)Bu(3))(2) (1(2)), was formed from [{(Me(3)Si)(2)N}Fe](2)(mu-N(SiMe(3))(2))(2) and the thiol, and its dissolution in THF generated ((t)Bu(3)SiS)(2)Fe(THF)(2) (1-(THF)(2)). Metathetical procedures with the thiolate yielded aggregate precursors [X(2)Fe](mu-SSi(t)Bu(3))(2)[FeX(THF)]Na(THF)(4) (3-X, X = Cl, Br) and cis-[(THF)IFe](2)(mu-SSi(t)Bu(3))(2) (4). Thermal desolvations of 3-Cl, 3-Br and 4 afforded molecular wheels [Fe(mu-X)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-FeX, X = Cl, Br) and the ellipse [Fe(mu-I)(mu-SSi(t)Bu(3))](14)(C(6)H(6))(n) (6-FeI). Related metathesis and desolvation sequences led to wheels [Co(mu-Cl)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-CoCl) and [Ni(mu-Br)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-NiBr). The nickel wheel disproportionated to give, in part, [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2) (7), which was also synthesized via salt metathesis. X-ray structural studies of 1(2) revealed a roughly planar Fe(2)S(4) core, while 1-(THF)(2), 3-Br, and 4 possessed simple distorted tetrahedral and edge-shared tetrahedral structures. X-ray structural studies revealed 5-MX (MX = FeCl, FeBr, CoCl, NiBr) to be wheels based on edge-shared tetrahedra, but while the pseudo-D(6)(d) wheels of 5-FeCl, 5-CoCl, and 5-FeBr pack in a body-centered arrangement, those of pseudo-C(6)(v)() 5-NiBr exhibit hexagonal packing and two distinct trans-annular d(Br...Br). Variable-temperature magnetic susceptibility measurements were conducted on 5-FeCl, 5-CoCl, 5-FeBr, and 6-FeI, and the latter three are best construed as weakly antiferromagnetic, while 5-FeCl exhibited modest ferromagnetic coupling. Features suggesting molecular magnetism are most likely affiliated with phase changes at low temperatures.     

Low-coordinate chromium siloxides: the "box" [Cr(mu-Cl)(mu-OSitBu3)]4, distorted trigonal [(tBu3SiO)3Cr][Na(benzene)] and [(tBu3SiO)3Cr][Na(dibenzo-18-c-6)], and trigonal (tBu3SiO)3Cr

Treatment of CrCl(2)(THF)(2) with NaOSi(t)Bu(3) afforded the tetrameric "box" [Cr(mu-Cl)(mu-OSi(t)Bu(3))](4) (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)(2) (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl(2)Cr(4-pic)(2) and trans-(silox)(2)Cr(4-pic)(x) (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(mu-Cl)(mu-OH)](4) (1') revealed that its singly occupied 3d orbitals spanned an energy range of approximately 2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na.C(6)H(6) (4, Y shaped, angle OCrO(Na) = 91.28(7) degrees), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)(3)Cr][Na(dibenzo-18-crown-6)] (5, angle OCrO = approximately 120 degrees, (120 + alpha) degrees, (120 - alpha) degrees). Calculations of [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na (4') and Cr(silox)(3)(-) (5') provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)(3)Cr (6) was synthesized from CrCl(3)(THF)(3) for structural and calculational comparisons to the chromous derivatives.     

Terminal nickel(ii) amide, alkoxide, and thiolate complexes containing amido diphosphine ligands of the type [N(o-C6H4PR2)2]- (R = Ph, (i)Pr, Cy)

A series of nickel(ii) complexes of the type [R-PNP]Ni(ER') ([R-PNP](-) = [N(o-C(6)H(4)PR(2))(2)](-); R = Ph, (i)Pr, Cy; E = NH, O, S; R' = Ph, (t)Bu) featuring unsupported, covalently bound pi-donor ligands have been prepared and characterized. The metathetical reactions of [R-PNP]NiCl (R = Ph, (i)Pr, Cy) with LiNHPh, NaOPh, or NaSPh, respectively, produced the corresponding anilide [R-PNP]Ni(NHPh), phenolate [R-PNP]Ni(OPh), and thiophenolate [R-PNP]Ni(SPh) derivatives. Treatment of [Ph-PNP]NiCl with either LiNH(t)Bu or NaO(t)Bu generated tert-butyl amide [Ph-PNP]Ni(NH(t)Bu) and tert-butoxide [Ph-PNP]Ni(O(t)Bu), respectively. In contrast, attempts to prepare analogous tert-butyl amide and tert-butoxide complexes of [(i)Pr-PNP](-) or [Cy-PNP](-) were not successful. Protonolysis studies of these nickel(ii)-heteroatom complexes revealed the basic reactivity of these pi-donor ligands. The basicity follows the order NH(t)Bu > O(t)Bu > NHPh > OPh > SPh. In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of [(i)Pr-PNP]Ni(NHPh) and [(i)Pr-PNP]Ni(OPh) are presented.     

Thermodynamics, kinetics, and mechanism of (silox)3M(olefin) to (silox)3M(alkylidene) rearrangements (silox = tBu3SiO; M = Nb, Ta)

Olefin complexes (silox)(3)M(ole) (silox = (t)Bu(3)SiO; M = Nb (1-ole), Ta (2-ole); ole = C(2)H(4), C(2)H(3)Me, C(2)H(3)Et, C(2)H(3)C(6)H(4)-p-X (X = OMe, H, CF(3)), C(2)H(3)(t)Bu, (c)C(5)H(8), (c)C(6)H(10), (c)C(7)H(10) (norbornene)) rearrange to alkylidene isomers (silox)(3)M(alk) (M = Nb (1=alk), Ta (2=alk); alk = CHMe, CHEt, CH(n)Pr, CHCH(2)C(6)H(4)-p-X (X = OMe, H, CF(3) (Ta only)), CHCH(2)(t)Bu, (c)C(5)H(8), (c)C(6)H(10), (c)C(7)H(10) (norbornylidene)). Kinetics and labeling experiments suggest that the rearrangement proceeds via a delta-abstraction on a silox CH bond by the beta-olefin carbon to give (silox)(2)RM(kappa(2)-O,C-OSi(t)Bu(2)CMe(2)CH(2)) (M = Nb (4-R), Ta (6-R); R = Me, Et, (n)Pr, (n)Bu, CH(2)CH(2)C(6)H(4)-p-X (X = OMe, H, CF(3) (Ta only)), CH(2)CH(2)(t)Bu, (c)C(5)H(9), (c)C(6)H(11), (c)C(7)H(11) (norbornyl)). A subsequent alpha-abstraction by the cylometalated "arm" of the intermediate on an alpha-CH bond of R generates the alkylidene 1=alk or 2=alk. Equilibrations of 1-ole with ole' to give 1-ole' and ole, and relevant calculations on 1-ole and 2-ole, permit interpretation of all relative ground and transition state energies for the complexes of either metal.     

Lithiation of tris(alkyl- and arylamido)orthophosphates EP[N(H)R]3 (E = O,S, Se): imido substituent effects and P=E bond cleavage

In the solid state, OP[N(H)Me](3) (1a) and OP[N(H)(t)Bu](3) (1b) have hydrogen-bonded structures that exhibit three-dimensional and one-dimensional arrays, respectively. The lithiation of 1b with 1 equiv of (n)BuLi generates the trimeric monolithiated complex (THF)[LiOP(N(t)Bu)[N(H)(t)Bu](2)](3) (4), whereas reaction with an excess of (n)BuLi produces the dimeric dilithium complex [(THF)(2)Li(2)OP(N(t)Bu)(2)[N(H)(t)Bu]](2) (5). Complex 4 contains a Li(2)O(2) ring in an open-ladder structure, whereas 5 embraces a central Li(2)O(2) ring in a closed-ladder arrangement. Investigations of the lithiation of tris(alkyl or arylamido)thiophosphates, SP[N(H)R](3) (2a, R = (i)Pr; 2b, R = (t)Bu; 2c, R = p-tol) with (n)BuLi reveal interesting imido substituent effects. For the alkyl derivatives, only mono- or dilithiation is observed. In the case of R = (t)Bu, lithiation is accompanied by P-S bond cleavage to give the dilithiated cyclodiphosph(V/V)azane [(THF)(2)Li(2)[((t)BuN)(2)P(micro-N(t)Bu)(2)P(N(t)Bu)(2)]] (9). Trilithiation occurs for the triaryl derivatives EP[N(H)Ar](3) (E = S, Ar = p-tolyl; E = Se, Ar = Ph), as demonstrated by the preparation of [(THF)(4)Li(3)[SP(Np-tol)(3)]](2) (10) and [(THF)(4)Li(3)[SeP(NPh)(3)]](2) (11), which are accompanied by the formation of small amounts of 10.[LiOH(THF)](2) and 11.Li(2)Se(2)(THF)(2), respectively.     

First row wheels, [((t)Bu(3)SiS)MX](12)(M = Co, X = Cl; M = Ni, X = Br), are common amongst both simpler and more complex aggregates

[((t)Bu(3)SiS)MX[(12) are wheels for first row transition metals (M = Co, X = Cl; M = Ni, X = Br), but for nickel, simpler [e.g. [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2)[ and more complicated [e.g. [(mu-SSi(t)Bu(3))Ni](5)(mu(5)-S)] structures are by-products.     

Cyclometalated products of [(COE)(2)RhCl](2) and 1,3-(RSCH(2))(2)C(6)H(4) (R = (t)Bu, (i)Pr) Are Dimeric. Synthesis,molecular structures,and solution dynamics of [mu-ClRh(H)(RSCH(2))(2)C(6)H(3)-2,6](2)

Two tridentate thioether pincer ligands, 1,3-(RSCH(2))(2)C(6)H(4) (R = (t)()Bu, 1a; R = (i)()Pr, 1b) underwent cyclometalation using [(COE)(2)RhCl](2) in air/moisture-free benzene at room temperature. The resultant complexes, [mu-ClRh(H)(RSCH(2))(2)C(6)H(3)-2,6](2) (R = (t)Bu, 2a; R = (i)Pr, 2b) are dimeric both in the solid state and in solution. A battery of variable-temperature one- and two-dimensional (1)H NMR experiments showed conclusively that both complexes undergo dynamic exchange in solution. Exchange between two dimeric diastereomers of 2a in solution occurred via rotation about the Rh-C(ipso) bond. The dynamic exchange of 2b was significantly more complex as an additional exchange mechanism, sulfur inversion, occurred, which resulted in the exchange between several diastereomers in solution.     

Insertion of H2C=CHX (X = F, Cl, Br, O(i)Pr) into (tBu3SiO)3TaH2 and beta-X-Elimination from (tBu3SiO)3HTaCH2CH2X (X = OR): relevance to Ziegler-Natta copolymerizations.

The insertion of H2C=CHX (X = OR; R = Me, Et, nPr, (i)Pr, CH=CH2, Ph) into (tBu3SiO)3TaH2 (1) afforded (tBu3SiO)3HTaCH2CH2X (2-CH2CH2X), which beta-X-eliminated to give ethylene and (tBu3SiO)3HTaX (3-X). beta-X-elimination rates were inversely proportional to the size of R. An X-ray crystallographic study of (tBu3SiO)3HTaCH2CH2O(t)Bu (2-CH2CH2O(t)Bu) revealed a distorted trigonal bipyramidal structure with an equatorial plane containing the hydride and a -CH2CH2O(t)Bu ligand with a staggered disposition. erythro- and threo-(tBu3SiO)3HTaCHDCHDOEt (2-CHDCHDOEt) are staggered in solution, according to (1)H NMR spectroscopic studies, and eliminated cis- and trans-HDC=CHD, respectively, helping verify the four-centered transition state for beta-OEt-elimination. When X = F, Cl, or Br, 2-CH2CH2X was not observed en route to 3-X, signifying that olefin insertion was rate-determining. Insertion rates suggested that substantial positive charge on the substituted carbon was incurred. The reactivity of other H2C=CHX with 1, and a discussion of the observations and their ramifications on the incorporation of functionalized monomers in Ziegler-Natta copolymerizations, are presented.     

Spin-state tuning at pseudotetrahedral d(7) ions: examining the structural and magnetic phenomena of four-coordinate [BP3]CoII-X systems

Electronic structure, spin-state, and geometrical relationships for a series of pseudotetrahedral Co(II) aryloxide, siloxide, arylthiolate, and silylthiolate complexes supported by the tris(phosphino)borate [BP(3)] ligands [PhBP(3)] and [PhBP(i)()(Pr)(3)] ([PhB(CH(2)PPh(2))(3)](-) and [PhB(CH(2)P(i)()Pr(2))(3)](-), respectively) are described. Standard (1)H NMR, optical, electrochemical, and solution magnetic data, in addition to low-temperature EPR and variable temperature SQUID magnetization data, are presented for the new cobalt(II) complexes [PhBP(3)]CoOSiPh(3) (2), [PhBP(3)]CoO(4-(t)()Bu-Ph) (3), [PhBP(3)]CoO(C(6)F(5)) (4), [PhBP(3)]CoSPh (5), [PhBP(3)]CoS(2,6-Me(2)-Ph) (6), [PhBP(3)]CoS(2,4,6-(i)()Pr(3)-Ph) (7), [PhBP(3)]CoS(2,4,6-(t)()Bu(3)-Ph) (8), [PhBP(3)]CoSSiPh(3) (9), [PhBP(3)]CoOSi(4-NMe(2)-Ph)(3) (10), [PhBP(3)]CoOSi(4-CF(3)-Ph)(3) (11), [PhBP(3)]CoOCPh(3) (12), [PhBP(i)()(Pr)(3)]CoOSiPh(3) (14), and [PhBP(i)()(Pr)(3)]CoSSiPh(3) (15). The low-temperature solid-state crystal structures of 2, 3, 5-10, 12, and 15 are also described. These pseudotetrahedral cobalt(II) complexes are classified as featuring one of two limiting distortions, either umbrella or off-axis. Magnetic and spectroscopic data demonstrate that both S = (1)/(2) and S = (3)/(2) ground-state electronic configurations are accessible for the umbrella distorted structure type, depending on the nature of the X-type ligand, its denticity (eta(1) versus eta(3)), and the tripodal phosphine ligand employed. Off-axis distorted complexes populate an S = (1)/(2) ground-state exclusively. For those four-coordinate complexes that populate S = (1)/(2) ground states, X-ray data show two Co-P bond distances that are invariably shorter than a third Co-P bond. The pseudotetrahedral siloxides 2, 10, and 11 are exceptional in that they display gradual spin crossover in the solid state. The diamagnetic cobalt(III) complex {[PhBP(3)]CoOSiPh(3)}{BAr(4)} ({16}{BAr(4)}) (Ar = Ph or 3,5-(CF(3))(2)-C(6)H(3)) has also been prepared and structurally characterized. Accompanying electronic structure calculations (DFT) for complexes 2, 6, and {16}(+) support the notion of a close electronic structure relationship between these four-coordinate systems and octahedral, sandwich, and half-sandwich coordination complexes.     

Oxygen extrusion from amidate ligands to generate terminal Ta=O units under reducing conditions. How to successfully use amidate ligands in dinitrogen coordination chemistry

A series of mixed Cp* amidate tantalum complexes Cp*Ta(RNC(O)R')X(3) (where R = Me(2)C(6)H(3), (i)Pr, R' = (t)Bu, Ph, X = Cl, Me) have been prepared via salt metathesis and their fundamental reactivities under reducing conditions have been explored. Reaction of the tantalum chloro precursors with potassium graphite under N(2) or Ar leads to the stereoselective formation of the terminal tantalum oxo species, Cp*Ta=O(η(2)-RN=CR')Cl. This represents the formal extrusion of oxygen from the amidate ligand to the reduced tantalum center and is accompanied by the formation of the iminoacyl fragment bound to Ta(v). Amidate dinitrogen complexes, [Cp*TaCl(RNC(O)(t)Bu)](2)(μ-N(2)) (where R = Me(2)C(6)H(3), (i)Pr) were synthesized via salt metathesis from the known [Cp*TaCl(2)](2)(μ-N(2)) precursor, establishing that amidate ligands can support dinitrogen complexes, but not the reduction process often necessary for their synthesis.     

Preparation, Crystal Structures, and Isomerization of the Tellurium Diimide Dimers RNTe(&mgr;-NR')(2)TeNR (R = R' = (t)Bu; R = PPh(2)NSiMe(3), R' = (t)Bu, (t)Oct): X-ray Structure of the Telluradiazole Dimer [(t)Bu(2)C(6)H(2)N(2)Te](2)

The reaction of R'NHLi (R = (t)Bu, (t)Oct) with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene at -78 degrees C, followed by warming to 23 degrees C, produces the tellurium diimide dimers RNTe(&mgr;-NR')(2)TeNR (2a, R' = (t)Bu, R = NPPh(2)NSiMe(3); 2b, R' = (t)Oct, R = NPPh(2)NSiMe(3)) and Ph(2)P(NHSiMe(3))(NSiMe(3)). X-ray analyses revealed that 2a and 2b have centrosymmetric structures containing a planar four-membered Te(2)N(2) ring and short exocyclic tellurium-nitrogen bond lengths (d(Te-N) = 1.900(5) and 1.897(4) or 1.905(4) ? for 2a and 2b, respectively). The exocyclic imido substituents adopt a trans arrangement with respect to the Te(2)N(2) ring. By contrast, the reaction of 2,4,6-(t)Bu(3)C(6)H(2)NHLi with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene under similar conditions produces the telluradiazole ((t)Bu(2)C(6)H(2)N(2)Te)(2) (3), which exists as a weakly associated dimer in the solid state with intramolecular Te-N distances of 2.628(4) ?. The tellurium diimide dimer (t)BuNTe(&mgr;-N(t)Bu)(2)TeN(t)Bu (2c'), prepared by the reaction of TeCl(4) with (t)BuNHLi in a 1:4 molar ratio, consists of a folded Te(2)N(2) ring with exocyclic N(t)Bu groups in a cis orientation. The (1)H, (31)P, and (125)Te NMR spectra of 2a and 2b indicate that the trans isomers slowly transform into the corresponding cis isomers in solution. Crystals of 2b are triclinic, space group P&onemacr; (No. 2), with a = 13.304(3) ?, b = 16.927(3) ?, c = 13.292(5) ?, alpha = 98.94(2), beta = 109.27(2), gamma = 69.04(2) degrees, V = 2636(1) ?(3), and Z = 4. The final R and R(w) values were 0.034 and 0.033, respectively. Crystals of 2c' are orthorhombic, space group Pnma (No. 62), with a = 9.535(3) ?, b = 14.264(3) ?, c = 16.963(4) ?, V = 2307.1(9) ?(3), and Z = 4. The final R and R(w) values were 0.040 and 0.040, respectively. Crystals of 3 are monoclinic, space group P2(1)/n (No. 14), with a = 9.117(3) ?, b = 11.481(4) ?, c = 16.550(4) ?, beta = 97.76(2) degrees, V = 1716.5(8) ?(3), and Z = 4. The final R and R(w) values were 0.031 and 0.034, respectively.     

Reactions of phosphonamidic acids and phosphonamidothioic acids with alcohols: mechanistic differences revealed by differing responses to steric effects

The formation of RP(X)(OH)OR' (R = Pr(i) or Bu(t), R' = Me or Pr(i)) from RP(X)(OH)NHBu(t) and R'OH in CDCl3 is insensitive to steric effects when X = S but not when X = O (> 10(3) times slower with R = Bu(t), R' = Pr(i) than with R = Pr(i), R' = Me), pointing to a dissociative elimination-addition mechanism (metathiophosphonate intermediate) when X = S but an associative S(N)2(P) mechanism when X = O.     

1,4-dioxobenzene compounds of gallium: reversible binding of pyridines to [[((t)Bu)(2)Ga](2)(mu-OC(6)H(4)O)](n) in the solid state

The gallium aryloxide polymer, [[((t)Bu)(2)Ga](2)(mu-OC(6)H(4)O)](n)(1) is synthesized by the addition of Ga((t)()Bu)(3) with hydroquinone in a noncoordinating solvent, and reacts with pyridines to yield the yellow compound [((t)()Bu)(2)Ga(L)](2)(mu-OC(6)H(4)O) [L = py (2), 4-Mepy (3), and 3,5-Me(2)py (4)] via cleavage of the Ga(2)O(2) dimeric core. The analogous formation of Ga((t)()Bu)(2)(OPh)(py) (5) occurs by dissolution of [((t)Bu)(2)Ga(mu-OPh)](2) in pyridine. In solution, 2-4 undergo dissociation of one of the pyridine ligands to yield [((t)()Bu)(2)Ga(L)(mu-OC(6)H(4)O)Ga((t)Bu)(2)](2), for which the DeltaH and DeltaS have been determined. Thermolysis of compounds 2-4 in the solid-state results in the loss of the Lewis base and the formation of 1. The reaction of 1 or [((t)Bu)(2)Ga(mu-OPh)](2) with the vapor of the appropriate ligand results in the solid state formation of 2-4 or 5, respectively. The deltaH and deltaS for both ligand dissociation and association for the solid-vapor reactions have been determined. The interconversion of 1 into 2-4, as well as [((t)Bu)(2)Ga(mu-OPh)](2) into 5, and their reverse reactions, have been followed by (13)C CPMAS NMR spectroscopy, TG/DTA, SEM, EDX, and powder XRD. Insight into this solid-state polycondensation polymerization reaction may be gained from the single-crystal X-ray crystallographic packing diagrams of 2-5. The crystal packing for compounds 2, 3, and 5 involve a head-to-head arrangement that is maintained through repeated ligand dissociation and association cycles. In contrast, when compound 4 is crystallized from solution a head-to-tail packing arrangement is formed, but during reintroduction of 3,5-Me(2)py in the solid state-vapor reaction of compound 1, a head-to-head polymorph is postulated to account for the alteration in the deltaH of subsequent ligand dissociation reactions. Thus, the deltaH for the condensation polymerization reaction is dependent on the crystal packing; however, the subsequent reversibility of the reaction is dependent on the polymorph.     

A neutral, monomeric germanium(I) radical

Stoichiometric reduction of the bulky β-diketiminato germanium(II) chloride complex [((But)Nacnac)GeCl] ((But)Nacnac = [{N(Dip)C(Bu(t))}(2)CH](-), Dip = C(6)H(3)Pr(i)(2)-2,6) with either sodium naphthalenide or the magnesium(I) dimer [{((Mes)Nacnac)Mg}(2)] ((Mes)Nacnac = [(MesNCMe)(2)CH](-), Mes = mesityl) afforded the radical complex [((But)Nacnac)Ge:](?) in moderate yields. X-ray crystallographic, EPR/ENDOR spectroscopic, computational, and reactivity studies revealed this to be the first authenticated monomeric, neutral germanium(I) radical.     

Redox reactions between phosphines (R3P; R = nBu, Ph) or carbene (iPr2IM) and chalcogen tetrahalides ChX4 (iPr2IM = 2,5-diisopropylimidazole-2-ylidene; Ch = Se, Te; X = Cl, Br)

The reactions between chalcogen tetrahalides (ChX(4); Ch = Se, Te; X = Cl, Br) and the neutral donors (n)Bu(3)P, Ph(3)P, or the N-heterocyclic carbene, 2,5-diisopropylimidazole-2-ylidene ((i)Pr(2)IM), have been investigated. In cases involving a phosphine, the chemistry can be understood in terms of a succession of two-electron redox reactions, resulting in reduction of the chalcogen center (e.g., Se(IV) --> Se(II)) and the oxidation of phosphorus to the [R(3)P-X] cation (P(III) --> P(V)). The stepwise reduction of Se(IV) --> Se(II) --> Se(0) --> Se(-II) occurs upon the successive addition of stoichiometric equivalents of Ph(3)P to SeCl(4), which can readily be monitored by 31P{(1)H} NMR spectroscopy. In the case of reacting SeX(4) with (i)Pr(2)IM, a similar two-electron reduction of the chalcogen is observed and there is the concomitant production of a haloimidazolium hexahaloselenate salt. The products have been comprehensively characterized, and the solid-state structures of [R(3)PX][SeX(3)] (9), [Ph(3)PCl](2)[TeCl(6)] (10), (i)Pr(2)IM-SeX(2) (11), and [(i)Pr(2)IM-Cl](2)[SeCl(6)] (12) have been determined by X-ray diffraction analysis. These data all support two electron redox reactions and can be considered in terms of the formal reductive elimination of X2, which is sequestered by the Lewis base.     

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.     

Mononuclear and dinuclear complexes with a [Ru(tBu2PCH2CH2PtBu2)(CO)] core

Thermolysis of solid [Ru(d(t)bpe)(CO)2Cl2](2, d(t)bpe =(t)Bu2PCH2CH2P(t)Bu2) under vacuum affords the five-coordinate complex [Ru(d(t)bpe)(CO)Cl2] (4), which was shown by X-ray crystallography to contain a weak remote agostic interaction. In solution, 4 can be readily trapped by CO, CH3CN or water to give [Ru(d(t)bpe)(CO)(L)Cl2](L = CO, 2; L = CH3CN, 6; L = H2O, 7). Reaction of 4 with AgOTf/H2O yields the tris-aqua complex [Ru(d(t)bpe)(CO)(H2O)3](OTf)2 (8), which has been structurally characterised and probed in solution by pulsed-gradient spin echo (PGSE) NMR spectroscopy. The water ligands in 8 are labile and easily substituted to give [Ru(d(t)bpe)(CO)(NCCH3)3](OTf)2 (10) and [Ru(d(t)bpe)(CO)(DMSO)3](OTf)2 (11). In the presence of CO, the tris-aqua complex undergoes water-gas shift chemistry with formation of the cationic hydride species [Ru(d(t)bpe)(CO)3H](OTf) (12) and CO2. X-Ray crystal structures of complexes 2, 4, 6, 8 and 11-12 are reported along with those for [{Ru(d(t)bpe)(CO)}2(mu-Cl)2(mu-OTf)](OTf) (3), [{Ru(d(t)bpe)(CO)}2(mu-Cl)3][Ru(d(t)bpe)(CO)Cl3](5) and [Ru(d(t)bpe)(CO)(H2O)2(OTf)](OTf)(9).     

The butterfly dimer [(tBu3SiO)Cr]2(mu-OSitBu3)2 and its oxidative cleavage to (tBu3SiO)2Cr(=N-N=CPh2)2 and (tBu3SiO)2Cr=N(2,6-Ph2-C6H3)

Treatment of CrCl2(THF)2 with NaOSitBu3 afforded the butterfly dimer [(tBu3SiO)Cr]2(mu-OSitBu3)2 (1(2)), whose d(CrCr) of 2.658(31) A and magnetism were indicative of strong antiferromagnetic coupling. A Boltzmann distribution of low-energy 1A1, 3B1, 5A1, 7B1, and 9A1 states obtained from calculations on [(HO)2Cr]2(muOH)2 (1'(2)) were used to provide a reasonable fit of the mu(eff) vs T data. Cleavage of 1(2) with various L (L = 4-picoline, p-tolunitrile, tBuCN, tBuNC, Ph2CO, and PMe3) generated (tBu3SiO)2CrL2 (1-L2). The dimer was oxidatively severed by Ph2CN2 to give (tBu3SiO)2Cr(N2CPh2)2 (2) and by RN3 at 23 degrees C to afford (silox)2Cr=NR (3-R) for bulky R (adamantyl (Ad), 2,6-iPr2-C6H3, 2,4,6-Me3-C6H2 = Mes, 2,6-Ph2-C6H3) and (tBu3SiO)2Cr(=NR)2 (4-R) for smaller substituents (R = 1-Naph, 2-Anth). X-ray structural studies were conducted on 1(2), square planar 1-(OCPh2)2, pseudo-Td 2 and pseudo-trigonal 3-(2,6-Ph2-C6H3), whose S = 1 ground state was discussed on the basis of calculations of (H3SiO)2Cr=NPh (3' '-Ph).     

3,5-Dimethyl and 3,5-di-tert-butylpyrazolato complexes with alkali metals: monomeric, dimeric, cluster, and 1D chain structures

The pyrazolato complexes [(Me(2)pz)(THF)Li] (1), [((t)Bu(2)pz)Li](4) (2), [((t)Bu(2)pzH)((t)()Bu(2)pz)Li](2) (2a), [(Me(2)pz)Na] (3), [((t)Bu(2)pz)Na](4), [((t)Bu(2)pz)(6)(OH)Na(7)] (4a), [((t)Bu(2)pz)(18-crown-6)Na] (4b), and [((t)Bu(2)pz)K] (5) were synthesized by metalation reactions between R(2)pzH (R = Me, (t)()Bu) and alkyllithium, elemental sodium, or potassium. All the complexes were characterized by spectroscopic methods and microanalysis, and in addition, the crystal structures of 2, 2a, 3, 4a, 4b, and 5 were obtained by single-crystal X-ray diffraction. They show monomeric, dimeric, cluster, and 1D chain structures in the solid state. Ab initio calculations on the structure and stabilities of the monomeric pzM complexes were performed at the MP2 level of theory showing good agreement with the coordination preferences of the pyrazolato ligand to a particular alkali ion.