Formation of Trinuclear Rhodium‐Hydride Complexes [{Rh(PP*)H}3‐ (μ2‐H)3(μ3‐H)][anion]2—During Asymmetric Hydrogenation?

Recently described and fully characterized trinuclear rhodium‐hydride complexes [{Rh(PP*)H}₃(μ₂‐H)₃(μ₃‐H)][anion]₂ have been investigated with respect to their formation and role under the conditions of asymmetric hydrogenation. Catalyst–substrate complexes with mac (methyl (Z)‐ N‐acetylaminocinnamate) ([Rh(tBu‐BisP*)(mac)]BF₄, [Rh(Tangphos)(mac)]BF₄, [Rh(Me‐BPE)(mac)]BF₄, [Rh(DCPE)(mac)]BF₄, [Rh(DCPB)(mac)]BF₄), as well as rhodium‐hydride species, both mono‐([Rh(Tangphos)‐ H₂(MeOH)₂]BF₄, [Rh(Me‐BPE)H₂(MeOH)₂]BF₄), and dinuclear ([{Rh(DCPE)H}₂(μ₂‐H)₃]BF₄, [{Rh(DCPB)H}₂(μ₂‐H)₃]BF₄), are described. A plausible reaction sequence for the formation of the trinuclear rhodium‐hydride complexes is discussed. Evidence is provided that the presence of multinuclear rhodium‐hydride complexes should be taken into account when discussing the mechanism of rhodium‐promoted asymmetric hydrogenation.     

Deprotonation induced ligand-to-metal electron transfer: synthesis of a mixed-valence Rh(-I,I) dinuclear compound and its reaction with dioxygen

Treatment of bis(2-picolyl)amine (bpa) with [{Rh(nbd)(mu-OMe)}2] leads to the unexpected and unique redox asymmetric dinuclear Rh-I,Rh+I complex [{Rh(nbd)}2(bpa-2H)] (2) with a pi-coordinating imine bound to a tetrahedral low valent rhodate(-I). Mono-oxygenation of the deprotonated bpa ligand in 2 by O2 leads to the mononuclear carboxamido complex [Rh(nbd)(bpam-H)] (3) (bpam = N-(2-picolyl)picolinamide). The second O atom of O2 ends up as a hydroxo fragment in [{Rh(nbd)(mu-OH)}2].     

Intramolecular alkyl phosphine dehydrogenation in cationic rhodium complexes of tris(cyclopentylphosphine)

[Rh(nbd)(PCyp(3))(2)][BAr(F) (4)] (1) [nbd = norbornadiene, Ar(F) = C(6)H(3)(CF(3))(2), PCyp(3) = tris(cyclopentylphosphine)] spontaneously undergoes dehydrogenation of each PCyp(3) ligand in CH(2)Cl(2) solution to form an equilibrium mixture of cis-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 a) and trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 b), which have hybrid phosphine-alkene ligands. In this reaction nbd acts as a sequential acceptor of hydrogen to eventually give norbornane. Complex 2 b is distorted in the solid-state away from square planar. DFT calculations have been used to rationalise this distortion. Addition of H(2) to 2 a/b hydrogenates the phosphine-alkene ligand and forms the bisdihydrogen/dihydride complex [Rh(PCyp(3))(2)(H)(2)(eta(2)-H(2))(2)][BAr(F) (4)] (5) which has been identified spectroscopically. Addition of the hydrogen acceptor tert-butylethene (tbe) to 5 eventually regenerates 2 a/b, passing through an intermediate which has undergone dehydrogenation of only one PCyp(3) ligand, which can be trapped by addition of MeCN to form trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(PCyp(3))(NCMe)][BAr(F) (4)] (6). Dehydrogenation of a PCyp(3) ligand also occurs on addition of Na[BAr(F) (4)] to [RhCl(nbd)(PCyp(3))] in presence of arene (benzene, fluorobenzene) to give [Rh(eta(6)-C(6)H(5)X){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (7: X = F, 8: X = H). The related complex [Rh(nbd){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] 9 is also reported. Rapid ( approximately 5 minutes) acceptorless dehydrogenation occurs on treatment of [RhCl(dppe)(PCyp(3))] with Na[BAr(F) (4)] to give [Rh(dppe){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (10), which reacts with H(2) to afford the dihydride/dihydrogen complex [Rh(dppe)(PCyp(3))(H)(2)(eta(2)-H(2))][BAr(F) (4)] (11). Competition experiments using the new mixed alkyl phosphine ligand PCy(2)(Cyp) show that [RhCl(nbd){PCy(2)(Cyp)}] undergoes dehydrogenation exclusively at the cyclopentyl group to give [Rh(eta(6)-C(6)H(5)X){PCy(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (17: X = F, 18: X = H). The underlying reasons behind this preference have been probed using DFT calculations. All the complexes have been characterised by multinuclear NMR spectroscopy, and for 2 a/b, 4, 6, 7, 8, 9 and 17 also by single crystal X-ray diffraction.     

Dinuclear rhodium and iridium complexes with mixed amido/methoxo and amido/hydroxo bridges

The reactions of [[M(mu-OMe)(cod)](2)] (M = Rh, Ir; cod = 1,5- cyclooctadiene) with p-tolylamine, alpha-naphthylamine, and p-nitroaniline gave complexes with mixed-bridging ligands, [[M(cod)](2)(mu-NHAr)(mu-OMe)]. Similarly, the related complexes [[Rh(cod)](2)(mu-NHAr)(mu-OH)] were prepared from the reactions of [[Rh(mu-OH)(cod)](2)] with p-tolylamine, alpha-naphthylamine, and p-nitroaniline. The reactions of [[Rh(mu-OR)(cod)](2)] (R = H, Me) with o-nitroaniline gave the mononuclear complex [Rh(o-NO(2)C(6)H(4)NH)(cod)]. The syntheses of the amido complexes involve a proton exchange reaction from the amines to the methoxo or hydroxo ligands and the coordination of the amide ligand. These reactions were found to be reversible for the dinuclear complexes. The structure of [[Rh(cod)](2)(mu-NH[p-NO(2)C(6)H(4)])(mu-OMe)] shows two edge-shared square-planar rhodium centers folded at the edge with an anti configuration of the bridging ligands. The complex [[Rh(cod)](2)(mu-NH[alpha-naphthyl])(mu-OH)] cocrystallizes with [[Rh(mu-OH)(cod)](2)] and THF, forming a supramolecular aggregate supported by five hydrogen bridges in the solid state. In the mononuclear [Rh(o-NO(2)C(6)H(4)NH)(cod)] complex the o-nitroamido ligand chelates the rhodium center through the amido nitrogen and an oxygen of the nitro group.     

Captured at last: a catalyst-substrate adduct and a Rh-dihydride solvate in the asymmetric hydrogenation by a Rh-monophosphine catalyst

The mechanism of asymmetric hydrogenation catalyzed by [Rh(NBD)((R)-PhenylBinepine)(2)]SbF(6)1 has been studied by NMR experiments and DFT computations. Either the low-temperature hydrogenation of the catalyst-substrate adduct 4 or the reaction of solvate dihydride 6 with MAC produced the hydrogenation product with over 99% ee (S).     

Square-planar rhodium(I) complexes partnered with [arachno-6-SB(9)H(12)]- : a route toward the synthesis of new rhodathiaboranes and organometallic/thiaborane salts

Treatment of [RhCl(eta4-diene)]2 (diene = nbd, cod) with the N-heterocyclic ligands 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and pyridine (py) followed by addition of Cs[arachno-6-SB9H12] affords the corresponding salts, [Rh(eta4-diene)(L2)][SB9H12] [diene = cod, L2 = bpy (1), Me2bpy (3), phen (5), (py)2 (7); diene = nbd, L2 = bpy (2), Me2bpy (4), phen (6), (py)2 (8)]. These compounds are characterized by NMR spectroscopy and mass spectrometry, and in addition, the cod-Rh species 1 and 3 are studied by X-ray diffraction analysis. These saltlike reagents are stable in the solid state, but in solution the rhodium(I) cations, [Rh(eta4-diene)(L2)]+, react with the polyhedral anion [SB9H12]- leading to a chemistry that is controlled by the d8 transition element chelates. The nbd-Rh(I) complexes react faster than the cod-Rh(I) counterparts, leading, depending on the conditions, to the synthesis of new rhodathiaboranes of general formulas [8,8-(L2)-nido-8,7-RhSB9H10] [L2 = bpy (9), Me2bpy (10), phen (11), (py)2 (12)] and [8,8-(L2)-8-(L')-nido-8,7-RhSB9H10] [L' = PPh3, L2 = bpy (13), Me2bpy (14), phen (15); L' = NCCH3, L2 = bpy (16), Me2bpy (17), phen (18)]. Compound 13 is characterized by X-ray diffraction analysis confirming the 11-vertex nido-structure of the rhodathiaborane analogues 14-18. In dichloromethane, 1 and 3 yield mixtures that contain the 11-vertex rhodathiaboranes 9 and 10 together with new species. In contrast, the cod-Rh(I) reagent 5 affords a single compound, which is proposed to be an organometallic rhodium complex bound exo-polyhedrally to the thiaborane cage. In the presence of H2(g) and stoichiometric amounts of PPh3, the cod-Rh(I) reagents, 1, 3, and 5, afford the salts [Rh(H)2(L2)(PPh3)2][SB9H12] [L2 = bpy (19), Me2bpy (20), phen (21)]. Similarly, in an atmosphere of CO(g) and in the presence of PPh3, compounds 1-6 afford [Rh(L2)(PPh3)2(CO)][SB9H12] (L2 = bpy (22), Me2bpy (23), phen (24)]. The structures of 19 and 24 are studied by X-ray diffraction analysis. The five-coordinate complexes [Rh(L2)(PPh3)2(CO)]+ undergo PPh3 exchange in a process that is characterized as dissociative. The observed differences in the reactivity of the nbd-Rh(I) salts versus the cod-Rh(I) analogues are rationalized on the basis of the higher kinetic lability of the nbd ligand and its faster hydrogenation relative to the cod diene.     

The complete characterization of a rhodium Lewis acid-dipolarophile complex as an intermediate for the enantioselective catalytic 1,3-dipolar cycloaddition of C,N-diphenylnitrone to methacrolein

The 1,3-dipolar cycloaddition reaction of C,N-diphenylnitrone with methacrolein is efficiently catalyzed by the rhodium diphosphine compound (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(H2O)](SbF6)2 [R-Prophos = (R)-(+)-1,2-bis(diphenylphosphino)-propane, 1.SbF6]; the asymmetric catalytic process occurs with reversal of regioselectivity, perfect endo selectivity, and up to 92% ee. The complete (NMR and X-ray analysis) characterization of the involved intermediate (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(methacrolein)](SbF6)2 (7.SbF6) allows us to interpret the observed selectivity.     

Selective oxygenation of amphiphilic thiacalix[3]pyridine Rh(I) diene complexes in both water and organic solvents

Thiacalix[3]pyridine (Py3S3) reacted with [Rh(diene)(mu-Cl)]2(diene = 1,5-cyclooctadiene (cod), 2,5-norbornadiene (nbd)) to give amphiphilic trigonal bipyramidal complexes, [Rh(Py3S3)(diene)]Cl. Sulfur bridges of the Py3S3 ligand in these complexes were selectively oxygenated by m-chloroperoxybenzoic acid in dichloromethane to give sulfinylcalix[3]pyridine complexes, [Rh(Py3(SO)3)(diene)]+, in which all three oxygen atoms of the SO groups occupy the equatorial positions. Structures of the complexes were analysed by X-ray crystallography and the oxidation reaction was investigated using 1H NMR spectroscopy and electrospray ionisation mass spectrometry showing that the oxygenation of the sulfur atoms in the ligand proceeded stepwise and further oxygenation of the SO moiety occurred only for the nbd complex having the smaller diene ligand resulting in [Rh(Py3(SO)2(SO2))(nbd)]+. On the other hand, the oxidation of [Rh(Py3S3)(cod)]+ by H2O2 in water did not result in oxygenation of the sulfur bridges but the cod ligand is hydroxygenated to give 1,4,5,6-eta4-2-hydroxycycloocta-4-ene-1,6-di-yl.     

Sulfur-bridged early-late heterobimetallics synthesized by incorporation of titanium,vanadium, and molybdenum into bis(hydrosulfido) templates of group 9 metals

Reactions of the bis(hydrosulfido) complexes [Cp*Rh(SH)(2)(PMe(3))] (1a; Cp* = eta(5)-C(5)Me(5)) with [CpTiCl(3)] (Cp = eta(5)-C(5)H(5)) and [TiCl(4)(thf)(2)] in the presence of triethylamine led to the formation of the sulfido-bridged titanium-rhodium complexes [Cp*Rh(PMe(3))(micro(2)-S)(2)TiClCp] (2a) and [Cp*Rh(PMe(3))(micro2-S)(2)TiCl(2)] (3a), respectively. Complex 3a and its iridium analogue 3b were further converted into the bis(acetylacetonato) complexes [Cp*M(PMe(3))(micro(2)-S)(2)Ti(acac)(2)] (4a, M = Rh; 4b, M = Ir) upon treatment with acetylacetone. The hydrosulfido complexes 1a and [Cp*Ir(SH)(2)(PMe(3))] (1b) also reacted with [VCl(3)(thf)(3)] and [Mo(CO)(4)(nbd)] (nbd = 2,5-norbornadiene) to afford the cationic sulfido-bridged VM2 complexes [(Cp*M(PMe(3))(micro2-S)(2))2V](+) (5a(+), M = Rh; 5b(+), M = Ir) and the hydrosulfido-bridged MoM complexes [Cp*M(PMe(3))(micro2-SH)(2)Mo(CO)(4)] (6a, M = Rh; 6b, M = Ir), respectively.     

Heteronuclear rhodium, palladium, platinum, and gold organoimido complexes from dinuclear organoamido rhodium precursors

Treatment of the organoamido complexes [Rh(2)(mu-4-HNC(6)H(4)Me)(2)(L(2))(2)] (L(2) = 1,5-cyclooctadiene (cod), L = CO) with nBuLi gave solutions of the organoimido species [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(L(2))(2)]. Further reaction of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(cod)(2)] with [Rh(2)(mu-Cl)(2)(cod)(2)] afforded the neutral tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(cod)(4)] (2), which rationalizes the direct syntheses of 2 from [Rh(2)(mu-Cl)(2)(cod)(2)] and Li(2)NC(6)H(4)Me. Reactions of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(CO)(4)] with chloro complexes such as [Rh(2)(mu-Cl)(2)(CO)(4)], [MCl(2)(cod)] (M = Pd, Pt), and [Ru(2)(mu-Cl)(2)Cl(2)(p-cymene)(2)] afforded the homo- and heterotrinuclear complexes PPN[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)] (5; PPN=bis(triphenylphosphine)iminium), [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)M(cod)] (M = Pd (6), Pt(7)) and [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)Ru(p-cymene)] (8), while the reaction with [AuCl(PPh(3))] gave the tetranuclear compound [(CO)(4)Rh(2)(mu--4-NC(6)H(4)Me)(2)[Au(PPh(3))](2)] (9). The structures of complexes 6, 8, and 9 were determined by X-ray diffraction studies. The anion of 5 reacts with [AuCl(PPh(3))] to give the butterfly cluster [[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)]Au(PPh(3))] (10), in which the Au atom is bonded to two rhodium atoms. Reaction of the anion of 5 with [Rh(cod)(NCMe)(2)](BF(4)) gave the tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(CO)(6)(cod)] (11) in which the Rh(cod) fragment is pi-bonded to one of the arene rings, while the reaction of the anion of 5 with [PdCl(2)(cod)] afforded the heterotrinuclear complex 6 through a metal exchange process.     

Bidentates versus monodentates in asymmetric hydrogenation catalysis: synergic effects on rate and allosteric effects on enantioselectivity

C 1-Symmetric phosphino/phosphonite ligands are prepared by the reactions of Ph 2P(CH 2) 2P(NMe 2) 2 with ( S)-1,1'-bi-2-naphthol (to give L A ) or ( S)-10,10'-bi-9-phenanthrol (to give L B ). Racemic 10,10'-bi-9-phenanthrol is synthesized in three steps from phenanthrene in 44% overall yield. The complexes [PdCl 2( L A,B )] ( 1a, b), [PtCl 2( L A,B )] ( 2a, b), [Rh(cod)( L A,B )]BF 4 ( 3a, b) and [Rh( L A,B ) 2]BF 4 ( 4a, b) are reported and the crystal structure of 1a has been determined. A (31)P NMR study shows that M, a 1:1 mixture of the monodentates, PMePh 2 and methyl monophosphonite L 1a (based on ( S)-1,1 '-bi-2-naphthol), reacts with 1 equiv of [Rh(cod) 2]BF 4 to give the heteroligand complex [Rh(cod)(PMePh 2)( L 1a )]BF 4 ( 5) and homoligand complexes [Rh(cod)(PMePh 2) 2]BF 4 ( 6) and [Rh(cod)( L 1a ) 2]BF 4 ( 7) in the ratio 2:1:1. The same mixture of 5- 7 is obtained upon mixing the isolated homoligand complexes 6 and 7 although the equilibrium is only established rapidly in the presence of an excess of PMePh 2. The predominant species 5 is a monodentate ligand complex analogue of the chelate 3a. When the mixture of 5- 7 is exposed to 5 atm H 2 for 1 h (the conditions used for catalyst preactivation in the asymmetric hydrogenation studies), the products are identified as the solvento species [Rh(PMePh 2)( L 1a )(S) 2]BF 4 ( 5'), [Rh(S) 2(PMePh 2) 2]BF 4 ( 6') and [Rh(S) 2( L 1a ) 2]BF 4 ( 7') and are formed in the same 2:1:1 ratio. The reaction of M with 0.5 equiv of [Rh(cod) 2]BF 4 gives exclusively the heteroligand complex cis-[Rh(PMePh 2) 2( L 1a ) 2]BF 4 ( 8), an analogue of 4a. The asymmetric hydrogenation of dehydroamino acid derivatives catalyzed by 3a, b is reported, and the enantioselectivities are compared with those obtained with (a) chelate catalysts derived from analogous diphosphonite ligands L 2a and L 2b , (b) catalysts based on methyl monophosphonites L 1a and L 1b , and (c) catalysts derived from mixture M. For the cinnamate and acrylate substrates studied, the catalysts derived from the phosphino/phosphonite bidentates L A,B generally give superior enantioselectivities to the analogous diphosphonites L 2a and L 2b ; these results are rationalized in terms of delta/lambda-chelate conformations and allosteric effects of the substrates. The rate of hydrogenation of acrylate substrate A with heterochelate 3a is significantly faster than with the homochelate analogues [Rh( L 2a )(cod)]BF 4 and [Rh(dppe)(cod)]BF 4. A synergic effect on the rate is also observed with the monodentate analogues: the rate of hydrogenation with the mixture containing predominantly heteroligand complex 5 is faster than with the monophosphine complex 6 or monophosphonite complex 7. Thus the hydrogenation catalysis carried out with M and [Rh(cod) 2]BF 4 is controlled by the dominant and most efficient heteroligand complex 5. In this study, the heterodiphos chelate 3a is shown to be more efficient and gives the opposite sense of optical induction to the heteromonophos analogue 5.     

Synthesis of [Ag(NH=CMe(2))(2)]ClO(4) and its use as a source of acetimine. 1. Synthesis of the first acetimine rhodium complexes and the first crystal structure of a diacetonamine complex

The reaction of AgClO(4) and NH(3) in acetone gave [Ag(NH=CMe(2))(2)]ClO(4) (1). The reactions of 1 with [RhCl(diolefin)](2) or [RhCl(CO)(2)](2) (2:1) gave the bis(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(2)]ClO(4) [diolefin = 1,5 cyclooctadiene = cod (2), norbornadiene = nbd (3)] or [Rh(CO)(2)(NH=CMe(2))(2)]ClO(4) (4), respectively. Mono(acetimine) complexes [Rh(diolefin)(NH=CMe(2))(PPh(3))]ClO(4) [diolefin = cod (5), nbd (6)] or [RhCl(diolefin)(NH=CMe(2))] [diolefin = cod (7), nbd (8)] were obtained by reacting 2 or 3 with PPh(3) (1:1) or with Me(4)NCl (1:1.1), respectively. The reaction of 4 with PR(3) (R = Ph, To, molar ratio 1:2) led to [Rh(CO)(NH=CMe(2))(PR(3))(2)]ClO(4) [R = Ph (9), C(6)H(4)Me-4 = To (10)] while cis-[Rh(CO)(NH=CMe(2))(2)(PPh(3))]ClO(4) (11) was isolated from the reaction of 1 with [RhCl(CO)(PPh(3))](2) (1:1). The crystal structures of 5 and [Ag[H(2)NC(Me)(2)CH(2)C(O)Me](PTo(3))]ClO(4) (A), a product obtained in a reaction between NH(3), AgClO(4), and PTo(3), have been determined.     

含半夹心结构铑的1,1'-二硫(硒、碲)二茂铁化合物

以半夹心结构铑的化合物Cp*Rh(CN^tBu)Cl2(1)(Cp*=η^5-C5Me5)与Fe(C5H4ELi)2.2THF反应,合成出异双核二茂铁化合物Cp*Rh(CN^tBu)(EC5H4)2Fe[E=S(2),Se(3),Te(4)]。通过AgBF4氧化2和3得到二茂铁离子型化合物[Cp*Rh(CN^tBu)(EC5H4)2Fe]BF4[E=S(5),Se(6)]。采用元素分析、红外光谱、^1H和13CNMR谱以及EI-MS表征了所合成的化合物。     

Synthesis, structure and theoretical study of two rhodium(I) complexes [Rh(TropNMe)(CO)(PPh3)] and [Rh(Trop)(CO)(PPh3)] · Acetone

Rhodium(I) complexes [Rh(TropNMe)(CO)(PPh₃)] (TropNMe = 2-(N-methylamino)tropone, ONC₈H₉) (1) and [Rh(Trop)(CO)(PPh₃)] · Acetone (Trop = Tropolone, O₂C₇H₆) (2) have been synthesized and characterized by single-crystal X-ray diffraction analysis. A distorted square planar geometry about the rhodium(I) metal centre is observed in both compounds 1 and 2. Substitution of an oxygen atom with a methyl functionalized nitrogen atom does not significantly alter the bond distances and angles in the rhodium(I) complex. A theoretical study at B3LYP/6-31G(d) (main group) and LANL2DZ (Rh) level is presented to clarify the solid state behaviour of these complexes.     

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(μ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.     

Arene-ruthenium complexes with salicyloxazolines: diastereoselective synthesis, configurational stability and applications as asymmetric catalysts for Diels-Alder reactions

Reaction of the dimers [RuCl2(eta6-arene)]2 (arene = benzene, p-cymene, mesitylene) with salicyloxazolines in the presence of NaOMe gives complexes [RuCl(R-saloxaz)(arene)] (1-5) which have been fully characterised. Complexes [RuL(iPr-saloxaz)(mes)]Y (L = py, 2-Mepy, 4-Mepy; PPh3; Y- = SbF6 or BPh4) 6-9 were prepared by treating the chloride 2a with ligand L and NaY (Y- = SbF6 or BPh4) in methanol at reflux. Halide complexes [RuX(iPr-saloxaz)(mes)](X = Br, 10; X = I, 11) were synthesised by treating 2a with AgSbF6 then with 1.2 equivalents of KBr or NaI, the methyl complex [RuMe(iPr-saloxaz)(mes)] 12 was synthesised from 2a by reaction with MeLi. Five complexes, [RuCl(iPr-saloxaz)(mes)] 2a, [RuCl(tBu-saloxaz)(p-cymene)] 3b, [RuCl(Ph-saloxaz)(mes)] 5a, [Ru(4-Mepy)(iPr-saloxaz)(mes)][SbF6] 7, and [Ru(PPh3)(iPr-saloxaz)(mes)][SbF6] 9, have been characterised by X-ray crystallography. Treatment of complexes 1-5 with AgSbF6 gives cationic species which are enantioselective catalysts for the Diels-Alder reaction of acroleins with cyclopentadiene, the effect of substituents on enantioselectivity has been examined.     

Synthesis, characterization, and reactivity of ruthenium diene/diamine complexes including catalytic hydrogenation of ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.     

Hydrogenation studies involving halobis(phosphine)-rhodium(I) dimers: use of parahydrogen induced polarisation to detect species present at low concentration

Reaction of [RhCl(PPh3)2]2 with parahydrogen revealed that the binuclear dihydride [Rh(H)2(PPh3)2mu-Cl)2Rh(PPh3)2] and the tetrahydride complex [Rh(H)2(PPh3)2(mu-Cl)]2 are readily formed. While magnetisation transfer from free H2 into both the hydride resonances of the tetrahydride and [Rh(H)2Cl(PPh3)3] is observable, neither transfer into [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] nor transfer between the two binuclear complexes is seen. Consequently [Rh(H)2(PPh3)2(mu-Cl)]2 and [Rh(H)2(PPh3)2(mu-Cl)2Rh(PPh3)2] are not connected on the NMR timescale by simple elimination or addition of H2. The rapid exchange of free H2 into the tetrahydride proceeds via reversible halide bridge rupture and the formation of [Rh(H)2(PPh3)2(mu-Cl)RhCl(H)2(PPh3)2]. When these reactions are examined in CD2Cl2, the formation of the solvent complex [Rh(H)2(PPh3)2(mu-Cl)2Rh(CD2Cl2)(PPh3)] and the deactivation products [Rh(Cl)(H)PPh3)2(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] and [Rh(Cl)(H)(CD2Cl2)(PPh3)(mu-Cl)(mu-H)Rh(Cl)(H)PPh3)2] is indicated. In the presence of an alkene and parahydrogen, signals corresponding to binuclear complexes of the type [Rh(H)2(PPh3)2(mu-Cl)(2)(Rh)(PPh3)(alkene)] are detected. These complexes undergo intramolecular hydride interchange in a process that is independent of the concentration of styrene and catalyst and involves halide bridge rupture, followed by rotation about the remaining Rh-Cl bridge, and bridge re-establishment. This process is facilitated by electron rich alkenes. Magnetisation transfer from the hydride ligands of these complexes into the alkyl group of the hydrogenation product is also observed. Hydrogenation is proposed to proceed via binuclear complex fragmentation and trapping of the resultant intermediate [RhCl(H)2PPh3)2] by the alkene. Studies on a number of other binuclear dihydride complexes including [(H)(Cl)Rh(PMe3)2(mu-H)(mu-Cl)Rh(CO)(PMe3)], [(H)2Rh(PMe3)2(mu-Cl)2Rh(CO)(PMe3)] and [HRh(PMe3)2(mu-H)(mu-Cl)2Rh(CO)(PMe3)] reveal that such species are able to play a similar role in hydrogenation catalysis. When the analogous iodide complexes [RhIPPh3)2]2 and [RhI(PPh3)3] are examined, [Rh(H)2(PPh3)2(mu-I)2Rh(PPh3)2], [Rh(H)2(PPh3)2(mu-I)]2 and [Rh(H)2I(PPh3)3] are observed in addition to the corresponding binuclear alkene-dihydride products. The higher initial activity of these precursors is offset by the formation of the trirhodium phosphide bridged deactivation product, [[(H)(PPh3)Rh(mu-H)(mu-I)(mu-PPh2)Rh(H)(PPh3)](mu-I)2Rh(H)2PPh3)2]     

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses,vibrational spectra,NMR studies,and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.     

On the reactivity toward ketones of new methyl amino complexes of Rh(III) and Ag(I). Synthesis of ortho-rhodiated acetophenone methyl imine complexes

MeNH(2) reacts with silver salts AgX (2:1) to give [Ag(NH(2)Me)(2)]X [X = TfO = CF(3)SO(3) (1.TfO) and ClO(4) (1.ClO(4))]. Neutral mono(amino) Rh(III) complexes [Rh(Cp*)Cl(2)(NH(2)R)] [R = Me (2a), To = C(6)H(4)Me-4 (2b)] have been prepared by reacting [Rh(Cp*)Cl(mu-Cl)](2) with RNH(2) (1:2). The following cationic methyl amino complexes have also been prepared: [Rh(Cp*)Cl(NH(2)Me)(PPh(3))]TfO (3.TfO), from [Rh(Cp*)Cl(2)(PPh(3))] and 1.TfO (1:1); [Rh(Cp*)Cl(NH(2)R)2]X, where R = Me, X = Cl, (4a.Cl), from [Rh(Cp*)Cl(mu-Cl)]2 and MeNH2 (1:4), or R = Me, X = ClO4 (4a.ClO4), from 4a.Cl and NaClO4 (1:4.8), or R = To, X = TfO (4b.TfO), from [Rh(Cp*)Cl(mu-Cl)](2), ToNH(2) and TlTfO (1:4:2); [Rh(Cp*)(NH(2)Me)(tBubpy)](TfO)(2) (tBubpy = 4,4'-di-tert-butyl-2,2'-bipyridine, 5.TfO), from 2a, TlTfO and tBubpy (1:2:1); [Rh(Cp*)(NH(2)Me)(3)](TfO)2 (6.TfO) from [Rh(Cp*)Cl(mu-Cl)](2) and 1.TfO (1:4). 2-6 constitute the first family of methyl amino complexes of rhodium. 1 and 4a.ClO(4) react with acetone to give, respectively, the methyl imino complexes [Ag{N(Me)=CMe(2)}()]X [X = TfO (7.TfO), ClO(4) (7.ClO(4))], and [Rh(Cp*)Cl(Me-imam)]ClO(4) [8.ClO(4), Me-imam = N,N'-N(Me)=C(Me)CH(2)C(Me)(2)NHMe]. 7.X (X = TfO, ClO(4)) are new members of the small family of methyl acetimino complexes of any metal whereas 8.ClO4 results after a double acetone condensation to give the corresponding bis(methyl acetimino) complex and an aldol-like condensation of the two imino ligands. The acetimino complex [Ag(NH=CMe(2))(2)]ClO(4) reacts with [Rh(Cp*)Cl(imam)]ClO(4) [1:1, imam = N,N'-NH=C(Me)CH(2)C(Me)(2)NH(2)] to give [Rh(Cp*)(imam)(NH=CMe(2))](ClO(4))(2) (9a.ClO(4)). 8.ClO(4) reacts with AgClO(4) (1:1) in MeCN to give [Rh(Cp*)(Me-imam)(NCMe)](ClO(4))2 (9b.ClO(4)), which in turn reacts with XyNC (Xy = C(6)H(3)Me(2)-2,6) or with MeNH(2) (1:1) to give [Rh(Cp*)(Me-imam)L](ClO(4))(2) [L = XyNC (9c.ClO(4)), MeNH(2) (9d.ClO(4))]. 6.TfO reacts with acetophenone to give [Rh(Cp*){C,N-C(6)H(4)C(Me)=N(Me)-2}(NH(2)Me)]TfO (10a.TfO), the first complex resulting from such a condensation and cyclometalation reaction. In turn, 10a.TfO reacts with isocyanides RNC (1:1) at room temperature to give [Rh(Cp*){C,N-C(6)H(4)C(Me)=NMe-2}(CNR)]TfO [R = tBu (10b.TfO), Xy (10c.TfO)], or 1:12 at 60 degrees C to give [Rh(Cp*){C,N-C(=NXy)C(6)H(4)C(Me)=N(Me)-2}(CNXy)]TfO (11.TfO). The crystal structures of 9a.ClO(4).acetone-d6, 9c.ClO(4), and 10a.TfO have been determined.