Gyroscope-like molecules consisting of three-spoke stators that enclose "switchable" neutral dipolar rhodium rotators; reversible cycling between faster and slower rotating Rh(CO)I and Rh(CO)2I species

trans-Rh(CO)(Cl)(P((CH(2))(14))(3)P) is prepared from trans-Rh(CO)(Cl)(P((CH(2))(6)CH[double bond, length as m-dash]CH(2))(3))(2) by a metathesis/hydrogenation sequence, and converted by substitution or addition reactions to Rh(CO)(I), Rh(CO)(2)(I), Rh(CO)(NCS), and Rh(CO)(Cl)(Br)(CCl(3)) species; the Rh(CO)(Cl) and Rh(CO)(I) moieties rapidly rotate within the cage-like diphosphine, but the other rhodium moieties do not.     

Thermomorphic fluorous phosphines as organocatalysts for Michael addition reactions

The fluorous phosphines P[(CH₂)_mR_fn]₃ (R_fn = (CF₂)_n−1CF₃; m/n = 2/8, 3/8, 3/10) are efficient nucleophilic catalysts of Michael addition reactions. They can be easily recycled based upon their highly temperature-dependent solubilities (thermomorphism), with recovery by simple liquid/solid phase separation. The phosphonium salt formed by reaction of the nucleophilic phosphine with the α,β-unsaturated system appears to be a significant component of the catalyst rest state.     

Preparation and properties of (η-C5H5)2ZrCl[Si(CH3)3] and (η-C5H5)2Zr[Si(CH3)3]2; trimethylsilyl group transfer from mercury to zirconium

Two silyl-zirconium compounds (η-C₅H₅)₂ZrCl[Si(CH₃)₃] (I) and (η-C₅H₅)₂-Zr[Si(CH₃)₃]₂ (II), have been prepared by the reaction of (η-C₅H₅)₂ZrCl₂ with Hg[Si(CH₃)₃]₂ in refluxing benzene. While I is unreactive toward 1-hexyne (55–60°C) and CO (350 psi), the zirconiumsilicon bond is cleaved by electrophiles such as Cl₂, HgCl₂, and AlCl₃.     

Bonding and electronic structure in consanguineous and conjugal iron and rhenium sp carbon chain complexes [MC4M'](n)+: computational analyses of the effect of the metal

Density functional theory has been used to probe the bonding and electronic properties of the homo- and heterobimetallic sp carbon chain complexes (ML(m), = (eta(5)-C(5)R(5))(eta(2)-R(2)PCH(2)CH(2)PR(2))Fe, (eta(5)-C(5)R(5))(NO)(PR(3))Re; z = 0-4). All neutral complexes are best described by MCtbd1;CCtbd1;CM electronic structures, in accord with much experimental data. The singlet dications are best described by cumulenic (+)M=C=C=C=C=M(+) valence formulations. However, the diiron and rhenium/iron dications are found to possess triplet states of nearly identical energy, clarifying experimental magnetic data. Their electronic structures have dominant *(+)MCtbd1;CCtbd1;CM(+)* character, with some spin delocalization onto the carbon chain. The mixed valence monocation radicals exhibit delocalized unpaired electrons, in accord with class III (strongly coupled) and II (weakly coupled) assignments made from experimental data earlier, with some spin density on the carbon chain. An isolable diiron trication has a doublet ground state, but some computational data suggest a close-lying quartet. For the unknown diiron tetracation, a bis(carbyne) or (2+)Fetbd1;CCtbd1;CCtbd1;Fe(2+) electronic structure is predicted. Calculated adiabatic ionization potentials show the iron endgroup to be more electron-releasing than rhenium, in accord with electrochemical data. This polarizes the electronic structures of the rhenium/iron complexes. To help validate the computed model structures, crystal structures of ((eta(5)-C(5)Me(5))Fe(eta(2)-dppe))(2)(mu-C(4)) and [((eta(5)-C(5)Me(5))Fe(eta(2)-dippe))(2)(mu-C(4))](3+) 3PF(6)(-) are determined. Data are analyzed with respect to related diruthenium and dimanganese complexes.     

Thermodynamic Enantioface-Binding Selectivities of Monosubstituted Alkenes to a Highly Discriminating Chiral Transition -Metal Lewis Acid; equilibration of diastereoisomeric (cyclopentadienyl)(alkene)(nitrosyl)(triphenylphosphine)rhenium complexes ([Re(η5–C5H5)(CH2 = CHR)(NO) (PPh3)]+BF)

Reactions of monosubstituted alkenes RCH = CH₂ and [Re(η⁵–C₅H₅)(CH₂Cl₂) (NO)(PPh₃)]⁺BF give complexes ([Re(η⁵–C₅H₅))(CH₂?CHR)(NO) (PPh₃)]⁺BF ( 1a–g ) in 63–99% yields as mixtures of (RS,SR)- and (RR,SS)-diastereoisomers ( 1a (R = Me), 66:34; 1b (R = Pr), 63:37; 1c (R = PhCH₂), 70:30; 1d (R = Ph), 75:25; 1e (R = i-Pr), 64:36; 1f (R = t-Bu), 84:16; 1g (R = Me₃Si), 69:31; Scheme 2). These differ in the C?C enantioface bound to the chiral Re fragment. In most cases, the analogous reactions of RCH?CH₂ and [Re(η⁵–C₅H₅) (C₆H₅Cl)(NO)(PPh₃)]⁺ BF give comparable results. When 1a – e , g are heated in PhCl at 95–100°, equilibration to 96:4, 97:3, 97:3, 90:10, > 99:< 1, and > 99:< 1 (RS,SR)/(RR,SS) mixtures occurs (79–99% recoveries; Tables 1 and 2). Thus, thermodynamic enantioface-binding selectivities are much higher than kinetic binding selectivities. This phenomenon is analyzed in detail. A crystal structure of (RS,SR)- 1e (monoclinic, P2₁/c, a = 10.256(1) Å. b = 17.191(1) Å, c = 16.191(1) Å, β = 101.04(1)°, Z = 4) shows that the Re–C(1)–C(2) plane (see Fig.2) is nearly coincident with the Re–P bond (angle 15°), and that the i-Pr group is ‘syn’ to the nitrosyl ligand.     

Theoretical study on the spin-state energy splittings and local spin in cationic [Re]-Cn-[Re] complexes

Total spin-state energy splittings are calculated for mono- and dications of the formula {[Re]-Cn-[Re]}z+ where [Re] = eta5-(C5Me5)Re(NO)(PPh3). Cn is an even-numbered carbon chain with n ranging from 4 to 20, and z is 1 or 2. These complexes are experimentally known, and their potential role as molecular electronic devices initiated this work. We have considered the different total spin states monocation/doublet, monocation/quartet, dication/singlet, and dication/triplet. Data obtained for two density functionals BP86 and B3LYP were compared to verify the internal consistency of the results. In both ionization states, the low-spin state is the ground state, but the spin-state splittings decrease as the chain gets longer. For the dications, the splitting reaches a nearly constant value of about 10 kJ/mol with BP86 and about 4 kJ/mol with B3LYP when there are at least 14 carbon atoms in the chain, whereas for the monocations, no constant value appears to be reached asymptotically, not even if 20 carbon atoms are in the chain. For monocations, the splittings range from 138 kJ/mol (n = 4) to 68 kJ/mol (n = 20) with BP86 and from 134 kJ/mol (n = 4) to 73 kJ/mol (n = 20) with B3LYP and are thus considerably higher than those of the dications. The spin-state splittings are qualitatively mirrored by the energy splitting between the highest-occupied molecular orbital with beta spin (HOMObeta) and the lowest-unoccupied molecular orbital with alpha spin (LUMOalpha) as obtained in the low-spin state. Furthermore, the HOMOalpha-LUMOalpha gaps decrease as the carbon chain lengthens. In addition, the local distribution of the ?z expectation value is analyzed for the monocation/doublet, the monocation/quartet, and the dication/triplet state using a modified L?wdin partitioning scheme. In the monocation/doublet and the dication/triplet state, the electron spin is distributed mainly on the metal centers and slightly delocalized onto the carbon chain. In the monocation/quartet state for chain lengths of more than 8 carbon atoms, the electron spin is mainly localized on selected atoms of the chain and not on the metal centers. In all cases, the spin delocalization onto the chain increases as the chain gets longer.     

Synthesis,structure, and reactivity of sp carbon chains with bis(phosphine) pentafluorophenylplatinum endgroups: butadiynediyl (C4) through hexadecaoctaynediyl (C16) bridges,and beyond

The reaction of trans-[(C(6)F(5))(p-tol(3)P)(2)PtCl] (PtCl) and butadiyne (cat. CuI, HNEt(2)) gives trans-[(C(6)F(5))(p-tol(3)P)(2)Pt(Ctbond;C)(2)H] (PtC(4)H, 81 %), which reacts with excess HC(triple bond)CSiEt(3) under Hay coupling conditions (O(2), cat. CuCl/TMEDA, acetone) to yield PtC(6)Si (53 %). A solution of PtC(6)Si in acetone is treated with wet nBu(4)NF to generate PtC(6)H. The addition of ClSiMe(3) (F(-) scavenger) and then excess HC(triple bond)CSiEt(3) under Hay conditions gives PtC(8)Si (39 %). Hay homocouplings of PtC(4)H, PtC(6)H, and PtC(8)H (generated in situ analogously to PtC(6)H) yield PtC(8)Pt, PtC(12)Pt, and PtC(16)Pt (97-92 %). Reactions of PtC(4)H and PtC(6)H with PtCl (cat. CuCl, HNEt(2)) give PtC(4)Pt and PtC(6)Pt (69 %, 34 %). The attempted conversion of PtC(8)H to PtC(10)Si affords mainly PtC(16)Pt, with traces of PtC(20)Pt and PtC(24)Pt. The complexes PtC(x)Pt are exceedingly stable (dec pts 234 to 288 degrees C), and Et(3)P displaces p-tol(3)P to give the corresponding compounds Pt'C(8)Pt' and Pt'C(12)Pt' (94-90 %). The effect of carbon chain lengths upon IR nu(C(triple bond)C) patterns (progressively more bands), UV/Vis spectra (progressively red-shifted and more intense bands with epsilon >600 000 M(-1) cm(-1)), redox properties (progressively more difficult and less reversible oxidations), and NMR values are studied, and analyzed with respect to the polymeric sp carbon allotrope "carbyne". The crystal structure of PtC(12)Pt shows a dramatic, unprecedented degree of chain bending, whereas the chains in PtC(8)Pt, Pt'C(12)Pt', and PtC(16)Pt are nearly linear.