Novel RhCp*/GaCp* and RhCp*/InCp* cluster complexes

The reaction of 6 equivalents of GaCp*(Cp*= pentamethylcyclopentadienyl) with [{Cp*RhCl2}2] yields the complex [Cp*Rh(GaCp*)3(Cl)2] (1) exhibting a cage-like intermetallic RhGa3 center with Ga-Cl-Ga bridges. Treatment of this complex with GaCl3 gives the Lewis acid-base adduct [Cp*Rh(GaCp*)2(GaCl3)]. (2) Reaction of [{Cp*RhCl2}2] with understoichiometric amounts of E(I)Cp*(E = Al, Ga, In) leads to a variety of products strongly dependent on the molecular ratio of the reactants. Thus, the reduction of [{Cp*RhCl2}2] with one equivalent of E(I)Cp*(E = Al, Ga, In) gives the RhII dimer [{Cp*RhCl}2]. The insertion of 3 equivalents of InCp* into the Rh-Cl bonds of [{Cp*RhCl2}2] yields the salt [Cp*2Rh]+[Cp*Rh(InCp*){In2Cl4(mu2-Cp*)}]- (3), the anion exhibiting an intermetallic RhIn(3) center with an intramolecularly bridging Cp* ring. The reaction of [{Cp*RhCl}2] with Cp*Ga yields various insertion products. In trace amount the "all hydrocarbon" cluster complex [(RhCp*)2(GaCp*)3] (6) is obtained. The corresponding ethylene containing cluster complex [{RhCp(GaCp*)(C2H4)}2] (7) can be prepared by treatment of [RhCp*(CH3CN)(C2H4)] with GaCp*.     

An eta(6)-dienyne transition-metal complex

The ruthenium complexes, [(eta5-C5R5)Ru(CH3CN)3]PF6 (1-Cp*, R = Me; 1-Cp, R = H), underwent reaction with both 1-(2-chloro-1-methylvinyl)-2-pentynyl-(Z)-cyclopentene (6-Z) and 1-(2-chloro-1-methylvinyl)-2-pentynyl-(E)-cyclopentene (6-E) to give (eta5-C5R5)Ru[eta6-(5-chloro-4-methyl-6-propylindan)]PF6 (7-Cp*, R = Me; 7-Cp, R = H). In a similar fashion, reaction of 1-Cp and 1-Cp* with 1-isopropenyl-2-pent-1-ynylcyclopentene (8) led to the formation of (eta5-C5R5)Ru(eta6-4-methyl-6-propylindan)]PF6 (9-Cp*, R = Me; 9-Cp, R = H). The reaction of 1-Cp* with 8 at -60 degrees C in CDCl3 solution led to observation of the eta6-dienyne complex, (eta5-C5Me5)Ru[eta6-(1-isopropenyl-2-pent-1-ynylcyclopentene)]PF6 (10), by 1H NMR spectroscopy. Complexes 7-Cp and 10 were characterized by X-ray crystallographic analysis.     

Isolation and characterization of a monomeric cationic titanium hydride

Methyl cations 1-Cp and 1-Cp*, stabilized by the tri-tert-butylphophinimine ligand and either C5H5 or C5Me5, were generated from the neutral dimethyl precursors and [Ph3C]+[B(C6F5)4]-. Reaction of these compounds with H2 resulted in contrasting reactions. For 1-Cp, hydrogenolysis of the Ti-CH3 group led to rapid reduction to Ti(III) and production of a cationic Ti(III) dimer, 2, presumably formed upon loss of H2 from a transiently generated Ti(IV) hydride. Compound 2 was characterized crystallographically and via its cleavage with donor solvents such as THF to form the monomeric [Cp(L)Ti(THF)2]+[B(C6F5)4]-, 3. In contrast, 1-Cp* reacted rapidly with H2 to form a cationic Ti(IV) hydride species, 4, which was resistant to reduction. While only moderately stable in solution under H2, a stable, isolable THF adduct preciptitated upon addition of THF, giving 4.THF, which was fully characterized, including via X-ray crystallography. Naked hydride 4 was very reactive toward haloarene solvents such as bromobenzene, giving the cationic bromide [Cp*(L)TiBr]+[B(C6F5)4]-, 5, which was fully characterized as its THF adduct 5.THF. The contrasting behavior of 1-Cp and 1-Cp* is a result of the greater steric protection and electron donation provided by the Cp* ligand relative to the Cp donor.     

Synthesis and rearrangements of aminosubstituted ferra- and ruthenatricarbaboranes

A room-temperature reaction between the [7-tBuNH-nido-7,8,9-C3B8H10]- anion (1a) and [Cp*RuCl]4 leads to the ruthenatricarbollide [1-Cp*-12-tBuNH-1,2,4,12-RuC3B8H10] (2) (yield 85%). Analogously, the room-temperature photochemical reaction of 1a with [CpFe(C6H6)]PF6 gives the previously reported iron complex [1-Cp-12-tBuNH-1,2,4,12-FeC3B8H10] (3) (yield 82%). Both reactions are associated with extensive polyhedral rearrangement, which occurs under very mild conditions and brings the carbon atoms to positions of maximum separation within the framework. Compounds 2 and 3 were also surprisingly obtained via complexation of the isomeric [8-tBuNH-nido-7,8,9-C3B8H10]- (1b) anion. Complex 2 rearranges further to [1-Cp*-10-tBuNH-1,2,4,10-RuC3B8H10] (4) upon refluxing in xylene (145 degrees C). Density functional theory calculations at the B3LYP/SDD level were used to estimate relative stabilities of these metallacarborane isomers. Compounds 2 and 4, along with the 11-vertex closo compounds [1-Cp*-1,2,3,10-RuC3B7H10] (5) and [1-Cp*-10-tBuNH-1,2,3,10-RuC3B7H9] (6), were also isolated from the reaction between [Cp*RuCl2]2 and 1a in boiling xylene. The structure of 2 was established by an X-ray diffraction study, and the constitution of all compounds was determined unambiguously by multinuclear NMR spectroscopy, mass spectrometry, and elemental analyses.     

Nickel dithiolene chelate rings in a new role as eta5-coordinating ligands: synthesis, structural characterization, and redox reactivity of an "Fe2Ni" bis-double-decker

A bis-double-decker complex has been assembled from the nickel bisdithiolene complex [Ni(S 2C 2Me 2) 2] (1-/2-) and two [Cp*Fe] (+) units (Cp* = C 5Me 5). The complex, [(eta (5)-Cp*-Fe-mu-eta (5),eta (5)-((S 2C 2Me 2) 2Ni)Fe-eta (5)-Cp*] ( n ) ( 1 ( n )), was isolated in two charge states ( n = 0, 1). The structure of 1 (+) was confirmed by X-ray crystallography for 1 (+)PF 6 (-) and 1 (+)BF 4 (-), and it shows the nickel bisdithiolene units pi-donating to iron centers. Both salts crystallize in a centrosymmetric space group (center of inversion at nickel). Computational (density functional theory) data indicate a highly delocalized spin density for 1 (+). The reaction of 1 with 1 or 2 equiv of HBF 4 leads to oxidation to form 1 (+) or 1 (2+), respectively. On an electrochemical time scale, reversibility is observed for the redox series 1/ 1 (+)/ 1 (2+), with an additional slower step for oxidation of 1 (2+).     

Group 14 triple-decker cations

The triple-decker cations trans-[(Cp*Sn)(2)(mu-eta(5):eta(5)-Cp*)](+) and trans-[(Cp*Pb)(2)(mu-eta(5):eta(5)-Cp*)](+) have been prepared and structurally characterized as their [B(C(6)F(5))(4)](-) salts from the reactions of [Cp*M][B(C(6)F(5))(4)](M = Sn, Pb) with the appropriate decamethylmetallocene. Both triple-decker cations adopt a cisoid arrangement of terminal Cp* groups, whereas the two known triple-decker main-group anions possess a transoid arrangement of terminal Cp groups. The reason for this conformational difference has been probed on the basis of DFT calculations.     

Pentamethylcyclopentadienyl-iridium(III) complexes with pyridylamino ligands: synthesis and applications as asymmetric catalysts for Diels-Alder reactions

Reaction of the dimer [(Cp*IrCl)2(P-Cl)2] with chiral pyridylamino ligands (pyam, L1-L5) in the presence of NaSbF6 gave complexes [Cp*IrCl(pyam)][SbF6] 1-5 as diastereomeric mixtures, which have been fully characterised, including the X-ray molecular structure determination of the complexes (S(Ir),R(N),R(C))-[Cp*IrClL1][SbF6] 1a and (R(Ir),S(N),S(C))-[Cp*IrClL5][SbF6] 5a. Treatment of these cations with AgSbF6 affords the corresponding aqua species [Cp*Ir(pyam)(H2O)][SbF6]2 6-10 which have been also fully characterised. The molecular structure of the complex (S(Ir),R(N),R(C))-[Cp*IrL,(H2O)][SbF6]2 6 has been determined by X-ray diffractometric methods. The aqua complexes [Cp*Ir(pyam)(H2O)][SbF6]2 (6, pyam = L2 (7), L3 (8)) evolve to the cyclometallated species [Cp*Ir{kappa3(N,N',C)-(R)-(C6H4)CH(CH3)NHCH2C5NH4}][SbF6] (11), [Cp*Ir{kappa3(N,N',C)-(R)-(C10H6)CH(CH3)-NHCH2C5NH4)}][SbF6] (12), and [Cp*Ir{kappa3(N,N',C)-(R)-(C10H6)CH(CH3)NHCH2C9NH6)}][SbF6] (13) respectively, via intramolecular activation of an ortho C-H aryl bond. Complexes 6-10 are enantioselective catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene. Reaction occurs rapidly at room temperature with good exo : endo selectivity (from 81 : 19 to 98 : 2) and moderate enantioselectivity (up to 72%). The involved intermediate Lewis acid-dienophile compounds [Cp*Ir(pyam)(methacrolein)][SbF]2 (pyam = L4 (14), L5 (15)) have been isolated and characterised.     

Mixed-transition-metal acetylides: synthesis and characterization of complexes with up to six different transition metals connected by carbon-rich bridging units

The synthesis and reaction chemistry of heteromultimetallic transition-metal complexes by linking diverse metal-complex building blocks with multifunctional carbon-rich alkynyl-, benzene-, and bipyridyl-based bridging units is discussed. In context with this background, the preparation of [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-(PPh(2))C(6)H(3)] (10) (dppf = 1,1'-bis(diphenylphosphino)ferrocene; tBu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridyl; Ph = phenyl) is described; this complex can react further, leading to the successful synthesis of heterometallic complexes of higher nuclearity. Heterotetrametallic transition-metal compounds were formed when 10 was reacted with [{(eta(5)-C(5)Me(5))RhCl(2)}(2)] (18), [(Et(2)S)(2)PtCl(2)] (20) or [(tht)AuC[triple bond]C-bpy] (24) (Me = methyl; Et = ethyl; tht = tetrahydrothiophene; bpy = 2,2'-bipyridyl-5-yl). Complexes [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-{PPh(2)RhCl(2)(eta(5)-C(5)Me(5))}C(6)H(3)] (19), [{1-[(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C]-3-[(tBu(2)bpy)(CO)(3)ReC[triple bond]C]-5-(PPh(2))C(6)H(3)}(2)PtCl(2)] (21), and [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-{PPh(2)AuC[triple bond]C-bpy}C(6)H(3)] (25) were thereby obtained in good yield. After a prolonged time in solution, complex 25 undergoes a transmetallation reaction to produce [(tBu(2)bpy)(CO)(3)ReC[triple bond]C-bpy] (26). Moreover, the bipyridyl building block in 25 allowed the synthesis of Fe-Ru-Re-Au-Mo- (28) and Fe-Ru-Re-Au-Cu-Ti-based (30) assemblies on addition of [(nbd)Mo(CO)(4)] (27), (nbd = 1,5-norbornadiene), or [{[Ti](mu-sigma,pi-C[triple bond]CSiMe(3))(2)}Cu(N[triple bond]CMe)][PF(6)] (29) ([Ti] = (eta(5)-C(5)H(4)SiMe(3))(2)Ti) to 25. The identities of 5, 6, 8, 10-12, 14-16, 19, 21, 25, 26, 28, and 30 have been confirmed by elemental analysis and IR, (1)H, (13)C{(1)H}, and (31)P{(1)H} NMR spectroscopy. From selected samples ESI-TOF mass spectra were measured. The solid-state structures of 8, 12, 19 and 26 were additionally solved by single-crystal X-ray structure analysis, confirming the structural assignment made from spectroscopy.     

Organometallic fragments coordinated to a multiisocyanide ligand and their physical properties

Preparation of a triisocyanide ligand, 1,3,5-tris[(4-isocyano-3,5-diisoproyl-phenyl)ethynyl]benzene (5), is presented. Ligand 5 is obtained in three steps in 76% overall yield. Reaction of 5 with (eta5-Cp*)Rh(Cabs,s')(Cabs,s'= 1,2-S2C2B10H10-S,S') produced the rhodadithiolene adduct [[(eta5-Cp*)Rh(Cabs,s')(CNC6H2iPr2-2,6-CC-3)]3C6H3-1,3,5] (6). Ligand 5 reacts with Cr(CO)5(THF) to give the triisocyanide complex [[Cr(CO)5(CNC6H2iPr2-2,6-CC-3)]3C6H3-1,3,5] (8) and with [AuCl(SMe2)] to give the triisocyanide complex [[AuCl(CNC6H2iPr2-2,6-CC-3)]3C6H3-1,3,5] (9). As revealed by a single-crystal X-ray diffraction study, the C(9)-N(3)-C(61) angle of 5.9 degrees of trichromium complex 8 occurs in the plane of the bridge and the gold center has a slightly bent linear configuration with a Cl(1)-Au(1)-C(21) angle of 175.4(4) degrees . The rhenation and platination of 5 employing [Re(bpy)(CO)3(AN)]PF6 (AN= acetonitrile) and [(CwedgeNwedgeN)PtCl] ((HCwedgeNwedgeN)= 6-phenyl-2,2'-bipyridine) yielded the luminescent Re(I) and Pt(II) complexes. Full characterization includes structural study of complexes 2, 8, and 9.     

Synthesis and characterization of heterometallic clusters (Ir2Rh, Ir2W, Rh3) Containing 1,2-dicarba-closo-dodecaborane(12)-1,2-dithiolate chelate ligands, [(B10H10)C2S2]2-

The 16-electron half-sandwich complex [Cp*Ir[S2C2(B10H10)]] (Cp* = eta5-C5Me5) (1a) reacts with [[Rh(cod)(mu-Cl)]2] (cod = cycloocta-1,5-diene, C8H12) in different molar ratios to give three products, [[Cp*Ir[S2C2(B10H9)]]Rh(cod)] (2), trans-[[Cp*Ir[S2C2(B10H9)]]Rh[[S2C2(B10H10)]IrCp*]] (3), and [Rh2(cod)2[(mu-SH)(mu-SC)(CH)(B10H10)]] (4). Complex 3 contains an Ir2Rh backbone with two different Ir-Rh bonds (3.003(3) and 2.685(3) angstroms). The dinuclear complex 2 reacts with the mononuclear 16-electron complex 1a to give 3 in refluxing toluene. Reaction of 1a with [W(CO)3(py)3] (py = C5H5N) in the presence of BF3.EtO2 leads to the trinuclear cluster [[Cp*Ir[S2C2(B10H10)]]2W(CO)2] (5) together with [[Cp*Ir(CO)[S2C2(B10H10)]]W(CO)5] (6), and [Cp*Ir(CO)[S2C2(B10H10)]] (7). Analogous reactions of [Cp*Rh[S2C2(B10H10)]] (1 b) with [[Rh(cod)(mu-Cl)]2] were investigated and two complexes cis-[[Cp*Rh[S2C2(B10H10)]]2Rh] (8) and trans-[[Cp*Rh[S2C2(B10H10)]]2Rh] (9) were obtained. In refluxing THF solution, the cisoid 8 is converted in more than 95 % yield to the transoid 9. All new complexes 2-9 were characterized by NMR spectroscopy (1H, 11B NMR) and X-ray diffraction structural analyses are reported for complexes 2-5, 8, and 9.     

One-step synthesis of alkenyl ketone complexes from Cp*RhCl2(PPh3), alkyne and H2O in the presence of KPF6

The reaction of Cp*RhCl2(PPh3) 1 with 1-alkyne and H2O in the presence of KPF6 afforded the alkenyl ketone complex [Cp*Rh(PPh3)(CPh=CHCOCH2R)](PF6) [R = p-tolyl (3a), R = Ph (3b)], whereas Cp*IrCl2(PPh3) 2 or [(eta 6-C6Me6)RuCl2(PPh3) gave the corresponding [Cp*IrCl(CO)(PPh3)](PF6) 5a and [(eta 6-C6Me6)RuCl(CO)(PPh3)](PF6).     

Metallaborane reactivity. A stoichiometric mechanism for the insertion of two alkynes into an iridaborane framework via a disposable molybdenum chaperone

Building on earlier work that showed the formation of [1-Cp*-2,2,2-(CO)3-2-THF-nido-1,2-IrMoB(4)H(8)], 2, from the reaction of [1-Cp*-arachno-1-IrB(4)H(10)], 1, with (arene)Mo(CO)3, the stoichiometric mechanism for the generation of [1-Cp*-5,6,7,8-(R)4-nido-1,5,6,7,8-IrC(4)B(3)H(3)], 8, from the reaction of 2 with RCCR, R = Me, Ph, has been identified. For R = Me, the major product in solution is [1-Cp*-5,6,7,8-(CH3)4-closo-1,5,6,7,8-IrC(4)B(3)H(3)Mo(CO)3], 7, which is in equilibrium with 8. The equilibrium 8 + Mo(THF)3(CO)3 <==> 7 + 3THF is characterized by DeltaH = 8 kcal/mol and DeltaS = 34 cal/mol K. Density functional theory calculations carried out on 7 indicate that the Mo(CO)3 moiety is weakly bound to the cluster mainly through Mo-C rather than Mo-B interactions. Under alkyne deficient conditions, the product [1-Cp*-2,2,2-(CO)3(mu-CO)-3,4-(CH3)2-closo-1,2,3,4-IrMoC(2)B(3)H(3)], 6, can be isolated. Solid-state structures of 1 and 2 have been reported previously, and those of 6, 7, and 8, R = Me, Ph, are reported here. The evolution of products with time was monitored by 1H and 11B NMR and showed the formation and decay of two additional species which have been identified as the structural isomers [1-Cp*-7,7,7-(CO)3-7-THF-2,3-(CH3)2-nido-1,7,2,3-IrMoC(2)B(3)H(5)], 4, and [5-Cp*-7,7,7-(CO)3-7-THF-2,3-(CH3)2-nido-5,7,2,3-IrMoC(2)B(3)H(5)], 5, with the metals nonadjacent in 4 and adjacent in 5. Circumstantial evidence suggests that 4 is the precursor to 5 and 5 is the precursor to both 6 and 7. Cluster 2 also is a catalyst or catalyst precursor for the isomerization of olefins, namely, hex-1-ene to cis-hex-2-ene and tetramethyl allene to 2,4-dimethylpenta-1,3-diene. These novel results also establish that [1-Cp*-2,2,2-(CO)3-2-(alkyne)-nido-1,2-IrMoB(4)H(8)], 3, forms from 2 and constitutes a logical precursor to 4. The entire process, 1 + 2alkyne = 8 + BH3 + 2H2, which is promoted by (arene)Mo(CO)3, constitutes an explicit example of a transition-metal-facilitated process analogous to metal-facilitated organic transformations observed in organometallic chemistry.     

The chemoselective reactions of tyrosine-containing G-protein-coupled receptor peptides with [Cp*Rh(H2O)3](OTf)2, including 2D NMR structures and the biological consequences

The bioconjugation of organometallic complexes with peptides has proven to be a novel approach for drug discovery. We report the facile and chemoselective reaction of tyrosine-containing G-protein-coupled receptor (GPCR) peptides with [Cp*Rh(H(2)O)(3)](OTf)(2), in water, at room temperature, and at pH 5-6. We have focused on three important GPCR peptides; namely, [Tyr(1)]-leu-enkephalin, [Tyr(4)]-neurotensin(8-13), and [Tyr(3)]-octreotide, each of which has a different position for the tyrosine residue, together with competing functionalities. Importantly, all other functional groups present, i.e., amino, carboxyl, disulfide, phenyl, and indole, were not prominent sites of reactivity by the Cp*Rh tris aqua complex. Furthermore, the influence of the Cp*Rh moiety on the structure of [Tyr(3)]-octreotide was characterized by 2D NMR, resulting in the first representative structure of an organometallic-peptide complex. The biological consequences of these Cp*Rh-peptide complexes, with respect to GPCR binding and growth inhibition of MCF7 and HT29 cancer cells, will be presented for [(η(6)-Cp*Rh-Tyr(1))-leu-enkephalin](OTf)(2) and [(η(6)-Cp*Rh-Tyr(3))-octreotide](OTf)(2).     

Iron complexes of facially capping triphosphorus macrocycles

Primary and secondary phosphine piano-stool complexes of the type [eta(5)-CpFeL3]+ (L = phenylphosphine, 3, (alpha-methyl)vinylphosphine, 4, allylphosphine, 5, (2-methylpropenyl)phosphine, 5b, allyl(phenyl)phosphine, 6) are described. The alkenyl phosphine complexes, 5 and 6, react by intramolecular hydrophosphination to give the corresponding [eta(5)-CpFe]+ complexes of 1,5,9-triphosphacyclododecane (12-aneP3R3, 2, R = H), 9 and 10 respectively. Alkylation of the secondary phosphines in 9 is achieved by hydrophosphinations with ethene to give the 12-aneP3R3 (R = Et) derivative 11. These complexes are also obtained by reaction of suitable [eta(5)-CpFe]+ containing precursor complexes with the corresponding free 12-aneP3R3 macrocycle as is the related [eta(5)-Cp*Fe]+ derivative, 8. Direct substitution of acetonitrile in [Fe(CH3CN)6][BF4]2 by 12-aneP3Et3, leads to the macrocycle piano-stool complex, [(12-aneP3Et3)Fe(CH3CN)3][BF4]2, 7. The crystal structures of selected primary phosphine, eta(5)-Cp, eta(5)-Cp* complexes and 7, allow a comparison of steric influences upon key macrocycle ring closure reactions and hence an insight into parameters required for the formation of smaller ring sizes by template based methods.     

A chiral stannate as an "ansa" pi-arene ligand in rhodium chemistry

Reaction of the triamido stannate MeSi[SiMe(2)N[(R)-CHMePh]](3)SnLi (1) with 0.5 molar equivalent of [RhCl(olefin)(2)](2) (olefin = COE, C(2)H(4)) or [RhCl(P(i)Pr(3))(2)](2) yielded the Rh-Sn complexes [MeSi[SiMe(2)N[(R)-CHMePh]](2)[SiMe(2)N[(R)-CHMe(eta(6)-C(6)H(5))]SnRh(L)] (L = COE: 2a, C(2)H(4): 2b, P(i)Pr(3) 3); their intramolecular eta(6)-coordination, along with the tin-rhodium bond, represents the first "ansa" pi-arene/stannate system.     

Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(eta5-C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(eta5-C5Me5)Ta}2B5H10(C6H4CH3)], and [{(eta5-C5Me5)TaCl}2B5H11

Reaction of [Cp*TaCl4] (Cp*=eta5-C5Me5) with a sixfold excess of LiBH(4)thf followed by BH3thf in toluene at 100 degrees C led to the isolation of hydrogen-rich metallaboranes [(Cp*Ta)2B4H10] (1), [(Cp*Ta)2B5H11] (2), [(Cp*Ta)2B5H10(C6H4CH3)] (3), and [(Cp*TaCl)2B5H11] (4) in modest yield. Compounds 1-3 are air- and moisture-sensitive but 4 is reasonably stable in air. Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron 4. Yellow tantalaborane 1 has a nido geometry with C2v symmetry and is isostructural with [(Cp*M)2B4H8] (M=Cr and Re); whereas 2 and 3 are C3v-symmetric and isostructural with [(Cp*M)2B5H9] (M=Cr, Mo, W) and [(Cp*ReH)2B5Cl5]. The most remarkable feature of 4 is the presence of a hydride ligand bridging the ditantalum center to form a symmetrical tantalaborane cluster with a long Ta--Ta bond (3.22 A). Cluster 4 is a rare example of electronically unsaturated metallaborane containing four TaHB bonds. All these new metallaboranes have been characterized by mass spectrometry, 1H, 11B, and 13C NMR spectroscopy, and elemental analysis, and the structural types were unequivocally established by crystallographic analysis of 1-4.     

Alpha-amino acids with metallocenyl side chains

A straightforward method for the synthesis of enantiomerically pure bis(valine)metallocenes is presented. Derivatives of lithium cyclopentadienylvaline 1a, b were obtained by addition of the (R)- or (S)-Sch?llkopf reagents to 6,6-dimethylfulvene as single enantiomers and gave with FeCl2 or [RuCl2(dmso)4] the chiral metallocenes [Fe[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2] (2a, b) and [Ru[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2] (3a, b). Complex 2b was hydrolyzed to the ferrocenylene-bis(valine-methylester) [[Fe[C5H4-CMe2-CH(NH3+)COOMe]2]2+(Cl-)2] (7) without racemization. Complex 7 could be used as ligand and was treated with [[Cp*IrCl2]2] to afford [Fe[C5H4-CMe2-CH(COOMe)(NH2-IrCp*Cl2)]2] (10). The reactions of 1 with CoCl2, [Re(CO)5Br], [[(cod)RhCl2]2] (cod= 1,5-cyclooctadiene) or [Cp*MCl3] (M= Ti, Zr) gave the cyclopentadienyl complexes [[Co[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2]+ I-] (11) and [Re[C5H4-CMe2-[C4H2N2(OMe)2iPr]](CO)3] (13), [(C8H12)Rh[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (14). [[Rh[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]I]2(mu-I)2] (15), [Cp*Cl2Ti-[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (16), and [Cp*Cl2Zr[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (17), with chiral valine derivatives as substituents on the cyclopentadienyl ring and with excellent diastereoselectivities. Also the Seebach reagent (Boc-BMI) or O'Donnell reagent could be added to 6,6-dimethylfulvene to give the lithium cyclopentadienides Li[C5H4-CMe2-[C3H2(tBu)(N-Boc)(NMe)O]] (18) and Li[C5H4-CMe2-CH(NCPh2)(COOEt)] (21), which formed the ferrocene derivatives [Fe[C5H4-CMe2-[C3H2(tBu)(N-Boc)(NMe)O]]2] (19) and [Fe[C5H4-CMe2-CH(NCPh2)(COOEt)]2] (22). The stable cobaltocinium cation in 11 and the complex 19 could be hydrolyzed to the metallocenes 12 and [Fe(C5H4-CMe2-CH(NH3+)(COO-)]2] (20) with two valines in the 1,1'-position. The structures of 2a, b, 11, 15, and 16 were determined by X-ray diffraction and confirm the diastereomeric purity of the compounds.     

Reactions of Pyridyl‐Functionalized,Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

Rh^III and Ir^III complexes based on the λ³‐P,N hybrid ligand 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine ( 1 ) react selectively at the P?C double bond to chiral coordination compounds of the type [( 1 H ? OH)Cp*MCl]Cl ( 2 , 3 ), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pK_a value of the P? OH group could be estimated. Whereas [( 1 H ? O)Cp*IrCl] ( 4 ) is formed quantitatively upon treatment with NEt₃, the corresponding rhodium compound [( 1 H ? O)Cp*RhCl] ( 5 ) undergoes tautomerization upon formation of the λ⁵σ⁴‐phosphinine rhodium(III) complex [( 1? OH)Cp*RhCl] ( 6 ) as confirmed by single‐crystal X‐ray diffraction. Blocking the acidic P? OH functionality in 3 by introducing a P? OCH₃ substituent leads directly to the λ⁵σ⁴‐phosphinine iridium(III) complex ( 8 ) upon elimination of HCl. These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition‐metal complexes containing λ⁵σ⁴‐phosphinine ligands.     

Syntheses of the 47 electron clusters [(Cp*Fe)3(mu3-X)2] (X = S, Se) and the First Fe/Sn/Se Heterocubane Cluster [(CpFe)3(SnCl3)(mu3-Se)4] x DME by the use of chalcogenostannate salts

By reacting 1-aminoethylammonium (H2NCH2CH2NH3+ = enH+) salts of [Sn2E6]4- anions (E = S, Se), [enH]4[Sn2S6] (1) and [enH]4[Sn2Se6] x en (2), with FeCl2/LiCp, three novel (partly) oxidized, Cp* ligated iron chalcogenide clusters were synthesized. Two of them, [(CpFe)3(mu3-S)2] (3) and [(Cp*Fe)3(mu3-Se)2] (4), contain formally 47 valence electrons. [(Cp*Fe)3(SnCl3)(mu3-Se)4] x DME (5) represents the first known mixed metal Fe/Sn/Se heterocubane type cluster. Compounds 3-5 were structurally characterized by single-crystal X-ray diffraction, and the odd valence electron number of the [Fe3E2] clusters (E = S, Se) was confirmed by density functional (DFT) investigations, mass spectrometry, cyclic voltammetry and a susceptibility measurement of 3.     

Structural and magnetic studies of the tris(cyclopentadienyl)manganese(II) "paddle-wheel" anions [Cp(3-n)(MeCp)(n)Mn](-) (n=0-3, MeCp=C(5)H(4)CH(3), Cp=C(5)H(5))

The ion-contact complexes [{(eta(5)-Cp)(2)Mn(eta(2):eta(5)-Cp)K}(3)]x0.5 THF (1x0.5 THF) and [{(eta(2)-Cp)(2)(eta(2);eta(5)-MeCp)MnK(thf)}]x2 THF (2x2 THF) and ion-separated complexes [Mg(thf)(6)][(eta(2)-Cp)(3)Mn](2) (3), [Mg(thf)(6)][(eta(2)-Cp)(eta(2)-MeCp)(2)Mn)](2)x0.5 THF (4x0.5 THF), [Mg(thf)(6)][(eta(2)-MeCp)(3)Mn)](2)x0.5 THF (5x0.5 THF) and [Li([12]crown-4)](5)[(eta-Cp)(3)Mn](5) (6) (Cp=C(5)H(5), CpMe=C(5)H(4)CH(3)), have been prepared and structurally characterised. The effects of varying the Cp and CpMe ligands in complexes 1-5 have been probed by variable-temperature magnetic susceptibility measurements and EPR spectroscopic studies.