Cyclopentadienyl complexes pentamethyl

The question How Much Steric Crowding Is Possible in Tris(q -pentamethyl-cyclopentadienyl) Complexes has been posed in a paper which describes the synthesis and structure of (C5Me5)3UCl and (C5Mes)3UF. The former of these structures is shown as 4. This follows work published by the same research group on the formation of [ (C5Me5)3U(C8H8) 2 (CsHs)] from cyclooctatetraene and... 

Two technical applications of C = N-X substrates have been reported. Noyori s Ru-PP-NN catalyst system was successfully applied in a feasibility study by Dow Chirotech for the hydrogenation of a sulfonyl amidine [77], while Avecia showed the commercial viability of its CATHy catalyst based on a pentamethyl cyclopentadienyl Rh complex for the reduction of phosphinyl imines [78] (Fig. 34.11). 

Scheme 43.3 Cofactor reduction using the pentamethyl cyclopentadienyl rhodium(bipyridine) complex (9/10).

When (40) is irradiated by Hg lamp at room temperature in the presence of pentamethyl-cyclopentadienyl dicarbonyl cobalt(III), Co(III) dithiolato complexes (45) and (46) are formed implying involvement of benzonitrile sulfide as an intermediate <92CL243). Thermolysis of (40) (and its phenyl ring substituted derivatives (40a)) at 110-140 °C in aromatic solvents results in formation of another heterocyclic mesoionic structure (47) and appears to proceed as a radical process (Scheme 2) (91TL4023). The reaction is inhibited by radical scavengers. 

The organometallic chemistry of the first-row transition metals generally starts with the binary metal carbonyl organometallic complexes. Noncarbonyl organometallic complexes starting with other easily accessible binary compounds provide entries to a broader spectrum of complexes. In this context, we describe the synthesis of the mixed sandwich complex (tj5-pentamethylcyclopentadienyl) ( j5-cyclopentadienyl) iron as an example of the synthetic utility of the solution-stable derivative (>j5-pentamethyl-cyclopentadienyl) (2,4-pentanedionate) iron. 

Neodymium cyclopentadienyl complexes are also obtained in-situ by the addition of Cp-derivatives (e.g. indene, cyclopentadiene, pentamethyl-cyclopentadiene, tetramethylcyclopentadiene, di-tert-butylcyclopentadiene, methylcyclopentadiene and fluorene) to standard Nd-catalyst systems such as NdV/MAO. It can be assumed that the respective cyclopentadienyl-anions are formed by proton abstraction from the Cp-derivatives. In the homopolymerization of BD the addition of Cp-derivatives results in an increase of the 1,2-content of about 4-10%. In addition, the in-situ formed Nd Cp-derivatives... 

An interesting variant in the family of cyclopentadienlyirid-ium complexes are those containing -mdenyl ligands. It had been shown by Mawby and coworkers that tndenyl metal complexes are far more reactive with respect to ligand snbstitntion chemistry than their cyclopentadienyl analognes." Basolo quantified this greatly accelerated reaction chemistry for a number of tndenyl metal systems and dubbed this acceleration the tndenyl effect . The tndenyl effect also appears to play an important role in the chemistry of indenyl iridium complexes. Indenyliridium complexes may be prepared in much the same way as the cyclopentadienyl and pentamethyl-cyclopentadienyl iridium complexes. However, once formed, they are far more reactive in terms of substitution chemistry. 

The formation constants of an actinium isopropyltropolonate complex were determined. Thermochemically relevant studies of thorium enolates generally involve bis(pentamethyl-cyclopentadienyl)thorium derivatives. Cp 2Th(Cl)(C(0)CFl2Bu-f) with an anionic acyl group that readily rearranges to the isomeric enolate Cp 2Th(Cl)OCH=CHBu-t. The Z-isomer is formed upon heating and the -isomer upon catalysis with Cp 2ThH2. Is the E or Z enolate thermodynamically more stable For the simple alkyl enolates MeCH=CHOR, the equilibration reaction of the Z- and E-isomers is nearly thermo-neutral . Consider the two species Cp 2Th(H)OCH(Bu-t)2 and Cp 2Th(H)0-2,6-C6H3 (Bu-f)2. The reversible addition of CO yields the rp- formyl derivative in reactions that are 19 4 and 25 6 kJmoR exothermic. These formyl species dimerize to form the classical enediolate, Cp 2Th(OR)OCH=CHO(OR)ThCp 2. This product is formed as the Z-isomer, plausibly thermodynamically preferred over the -isomer, much as (Z)-MeOCH=CHOMe is preferred over its E-counterpart by 6.0 0.2 kJmoR. ... 

R366 M. Herberhold, A. M. Dietel, J. Peuker, A. Pfeifer and W. Milius, Sandwich and Half-Sandwich Complexes Derived from Pentamethyl-cyclopentadienyl Tetracarbonyl Vanadium, Cp V(CO)4 , Appl Orga-nomet. Chem., 2000,14, 519... 

In spite of low levels of the "Cr(CO)3Cp radical present in solution under typical conditions, it was soon realized that the increased reactivity of the Cr-Cr complex could be assigned unequivocally to the presence, albeit in small amounts, of this highly reactive radical. Compared to the cyclopentadienyl system, the pentamethyl-cyclopentadienyl dimer (which exists in the solid state as a Cr-Cr-bonded dimer) is more extensively dissociated than the unsubstituted cyclopentadienyl system ... 

We have, over the past few years, been developing a new series of homogeneous catalysts that do not contain such phosphine or phosphite ligands (and that are indeed deactivated by them), based on pentamethyl-cyclopentadienyl-rhodium and -iridium compounds. The parent complexes [M(C5Me5)Cl2]2 (1, M = Rh or Ir) are readily obtained from hexamethyl Dewar benzene and the appropriate hydrated metal chloride in a two-step reaction (2). 

For gas-phase ion-molecule reactions with small translational energies, the electrostatic attractions (e.g., ion-dipole) result in collision complexes with finite lifetimes, and a PE well in translational space that contains the electron transfer reaction coordinate (see Figure 6). In order for the comparison to solution studies to be meaningful, must be longer than the lifetime required for vibrational relaxation and electron transfer. These criteria are satisfied for reactions of bis-cyclopentadienyl (Cp Cp designates the pentamethyl-cyclopentadienyl ligand) complexes Equation (64),... 

In 1992 Yasuda et al. [236, 237] reported that organolanthanide complexes of the type Cp 2Sm-R (where Cp is pentamethyl cyclopentadienyl, and R is either an alkyl, alkylaluminum or a hydride) initiate highly syndiotactic, living polymerizations of methacrylates. It was also reported that lanthanide complexes such as Cp 2Yb(THF)i 3, Cp 2Sm(THF)2, and (indenyl)2Yb(THF)2 can also initiate polymerizations of methylmethacrylate [238]. Although very low initiator efficiencies were... 

The most efficient systems are based on arene Ru(II) or pentamethyl-cyclopentadienyl Rh(HI) complexes with the chiral ligands depicted in Figure 90. Sodium formate is used as the hydrogen source (355-357). In the reduction of AT-sulfonylimines (HI), higher reactivity was observed when formic acid-triethylamine azeotrope was used as the hydrogen donor, probably due to the... 

In the transition metal series, cowdinatively unsaturated complexes, e.g. with d configuration, can pose similar problems steric shielding of axial positions by T) -mesityl or Ti -pentamethyl-cyclopentadienyl can to some extent stabilize reactive oxidized states such as Pt(III) [8] or highly reduced intermediates such as electron-rich and reactive Rh(I)/ Rh(0) [9] or Ir(I)/ Ir(0) (2, cf. Section 3). 

Dinuclear complexes in which the two metal atoms are bridged by polyyne, unsaturated elemental carbon chains (15-17), have received considerable attention due to their unique properties. For example, upon oxidation, these complexes form metallacumulenes of the general formula [L M=(C=C)p=ML ] +, where L includes pentamethyl-cyclopentadienyl, [Cp, C5(CH3)5], triarylphosphine, [Ar3 , Ar = Ph, C6H5, and Tol, P-CH3C6H4], aryl, CO, and NO. With the fragment [C5(CH3)5]Re(NO)[P (05115)3] as the capping, complex molecules with chains containing up to 20 carbon atoms have been synthesized. For compound 17 a rhenium-rhenium distance of 2.87 nm was estimated. These complexes can be considered the first step toward metal-capped, one-dimensional carbon allotropes. 

A heterodinuclear iridium-ruthenium complex [Ir (Cp )(H20)-(bpm)Ru (bpy)2](S04)2 (Ir -OH2, Cp = j -pentamethyl-cyclopentadienyl, bpm = 2,2 -bipyrimidine, bpy = 2,2 -bipyridine) can also act as an effective catalyst for removal of dissolved O2 by the four-electron reduction of O2 with formic acid in water at an ambient temperature. The Ir complex reacts efficiently with O2, as shown by the spectral titration in Figure 4.24, where the absorption spectra due to Ir are changed to those of Ir -OH2. The titration... 

Manriquez JM, Bercow JE (1974) Preparation of a dinitrogen complex of bis(pentamethyl-cyclopentadienyl)zirconium(II). Isolation and protonation leading to stoichiometric reduction of dinitrogen to hydrazine. J Am Chem Soc %(19) 6229-6230... 

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