Redox-Transmetalation Reactions: Easy Access to Homo- and Heterodimetallic d,d Complexes.

The ability of the imine PyCH═N-CHPy (Py = 2-pyridyl, bpi) to behave as a heteroditopic ligand, which is suitable for creating two separate compartments to host metals in different oxidation states, has been developed by studying the reactions of the mixed-valence complexes [(cod)M(μ-bpi)M(cod)] (M = Rh, Ir) with [M'(Cl)(PPh)] (M' = Pd, Ni). The results depend on the molar ratio of the reagents used (1:1 or 1:2) to give the heterometallic complexes {d-M',d-M}-[(PPh)(Cl)M'(μ-bpi)M(cod)] (Pd,Rh, ; Pd,Ir, ; Ni,Rh, ; Ni,Ir, ) and the two-electron mixed-valent compounds [(PPh)(Cl)M'(μ-bpi)M'(Cl)] (M' = Ni, ; Pd, ), respectively. A redox process occurs in the replacement of the low-valent [(cod)M] fragment, whereas the exchange of the [(cod)M] fragment is redox-neutral.

Mixed-Valence Tetrametallic Iridium Chains.

Neutral [X-{Ir }-{Ir }-X] (X=Cl, Br, SCN, I) and dicationic [L-{Ir }-{Ir }-L] (L=MeCN, Me CO) tetrametallic iridium chains made by connecting two dinuclear {Ir } units ({Ir }=[Ir (μ-OPy) (CO) ], OPy=2-pyridonate) by an iridium-iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain.

Iridium-Catalyzed Regio- and Diastereoselective Synthesis of C-Substituted Piperazines.

Piperazine rings are essential motifs frequently found in commercial drugs. However, synthetic methodologies are mainly limited to -substituted piperazines, preventing structural diversity. Disclosed herein is a straightforward catalytic method for the synthesis of complex C-substituted piperazines based on an uncommon head-to-head coupling of easily prepared imines.

Rhodium Complexes in P-C Bond Formation: Key Role of a Hydrido Ligand.

Olefin hydrophosphanation is an attractive route for the atom-economical synthesis of functionalized phosphanes. This reaction involves the formation of P-C and H-C bonds. Thus, complexes that contain both hydrido and phosphanido functionalities are of great interest for the development of effective and fast catalysts.

Three-Coordinate Rhodium Complexes in Low Oxidation States.

The isolation of simultaneously low-coordinate and low-valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri-coordinate rhodium(-I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ-Cl)(IPr)(dvtms)} ] (1, IPr=1,3-bis(2,6-diisopropylphenyl)imidazolyl-2-ylidene; dvtms=divinyltetramethyldisiloxane) with KC gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)] results from their oxidation or by abstraction of chloride from 1 with silver salts.

Rhodium Complexes in P-H Bond Activation Reactions.

The feasibility of oxidative addition of the P-H bond of PHPh to a series of rhodium complexes to give mononuclear hydrido-phosphanido complexes has been analyzed. Three main scenarios have been found depending on the nature of the L ligand added to [Rh(Tp)(C H )(PHPh )] (Tp= hydridotris(pyrazolyl)borate): i) clean and quantitative reactions to terminal hydrido-phosphanido complexes [RhTp(H)(PPh )(L)] (L=PMe , PMe Ph and PHPh ), ii) equilibria between Rh and Rh species: [RhTp(H)(PPh )(L)]⇄[RhTp(PHPh )(L)] (L=PMePh , PPh ) and iii) a simple ethylene replacement to give the rhodium(I) complexes [Rh(κ -Tp)(L)(PHPh )] (L=NHCs-type ligands). The position of the P-H oxidative addition-reductive elimination equilibrium is mainly determined by sterics influencing the entropy contribution of the reaction.

Inner-Sphere Oxygen Activation Promoting Outer-Sphere Nucleophilic Attack on Olefins.

Alkoxylation and hydroxylation reactions of 1,5-cyclooctadiene (cod) in an iridium complex with alcohols and water promoted by the reduction of oxygen to hydrogen peroxide are described. The exo configuration of the OH/OR groups in the products agrees with nucleophilic attack at the external face of the olefin as the key step. The reactions also require the presence of a coordinating protic acid (such as picolinic acid (Hpic)) and involve the participation of a cationic diolefin iridium(III) complex, [Ir(cod)(pic) ] , which has been isolated.

Activating a Peroxo Ligand for C-O Bond Formation.

Dioxygen activation for effective C-O bond formation in the coordination sphere of a metal is a long-standing challenge in chemistry for which the design of catalysts for oxygenations is slowed down by the complicated, and sometimes poorly understood, mechanistic panorama. In this context, olefin-peroxide complexes could be valuable models for the study of such reactions. Herein, we showcase the isolation of rare "Ir(cod)(peroxide)" complexes (cod=1,5-cyclooctadiene) from reactions with oxygen, and then the activation of the peroxide ligand for O-O bond cleavage and C-O bond formation by transfer of a hydrogen atom through proton transfer/electron transfer reactions to give 2-iradaoxetane complexes and water.

Pseudo-tetrahedral Rhodium and Iridium Complexes: Catalytic Synthesis of E-Enynes.

The reactions of the rhodium(I) and iridium(I) complexes [M(PhBP )(C H )(NCMe)] (PhBP =PhB(CH PPh ) ) with alkynes have resulted in the synthesis of a new family of pseudo-tetrahedral complexes, [M(PhBP )(RC≡CR')] (M=Rh, Ir), which contain the alkyne as a four-electron donor. The reactions of these unusual compounds with two-electron donors (L=PMe , CNtBu) produced a change in the "donicity" of the alkyne from a 4e to a 2e donor to give five-coordinate complexes. These were the final products with the iridium complexes, whereas further reactions took place with the rhodium complexes.

Rhodium Complexes Promoting C-O Bond Formation in Reactions with Oxygen: The Role of Superoxo Species.

C-O bond formation in reactions of olefins with oxygen is a long standing challenge in chemistry for which the very complicated-sometimes controversial-mechanistic panorama slows down the design of catalysts for oxygenations. In this regard, the mechanistic details of the oxidation of the complex [Rh(cod)(Ph N )] (1) (cod=1,5-cyclooctadiene) with oxygen to the unique 2-rhodaoxetane compound [{Rh(OC H )(Ph N )} ] (2) has been investigated by DFT calculations. The results of this study provide evidences for a novel bimetallic mechanism in which two rhodium atoms redistribute the four electrons involved in the cleavage of the O=O bond.

Nucleophilicity and P-C Bond Formation Reactions of a Terminal Phosphanido Iridium Complex.

The diiridium complex [{Ir(ABPN2)(CO)}2(μ-CO)] (1; [ABPN2](-) = [(allyl)B(Pz)2(CH2PPh2)](-)) reacts with diphenylphosphane affording [Ir(ABPN2)(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H(+), Me(+), and O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN2)(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P-C bond formation, depending on the reaction conditions.

Terminal phosphanido rhodium complexes mediating catalytic P-P and P-C bond formation.

Complexes with terminal phosphanido (M-PR2) functionalities are believed to be crucial intermediates in new catalytic processes involving the formation of P-P and P-C bonds. We showcase here the isolation and characterization of mononuclear phosphanide rhodium complexes ([RhTp(H)(PR2)L]) that result from the oxidative addition of secondary phosphanes, a reaction that was also explored computationally. These compounds are active catalysts for the dehydrocoupling of PHPh2 to Ph2P-PPh2.

Terminal imido rhodium complexes.

Compounds of the late transition metals with M=X multiple bonds (X=CR2, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second- and third-row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP3)(NR)] (PhBP3=PhB{CH2PPh2}3) with a multiple and terminal Rh=N bond.

Pseudotetrahedral rhodium(I) complexes.

A combination of four-electron donors, such as alkynes, with strongly donating and strong-field scorpionate ligands is appropriate to create pseudotetrahedral rhodium(I) environments, as found in [Rh(PhBP3 )(HCCPh)], which promotes HC bond activation and CC coupling reactions under very smooth conditions.

Cooperative double deprotonation of bis(2-picolyl)amine leading to unexpected bimetallic mixed valence (M(-I), M(I)) rhodium and iridium complexes.

Cooperative reductive double deprotonation of the complex [Rh(I)(bpa)(cod)](+) ([4](+), bpa = PyCH(2)NHCH(2)Py) with one molar equivalent of base produces the bimetallic species [(cod)Rh(bpa-2H)Rh(cod)] (7), which displays a large Rh(-I),Rh(I) contribution to its electronic structure. The doubly deprotonated ligand in 7 hosts the two "Rh(cod)" fragments in two distinct compartments: a "square planar compartment" consisting of one of the Py donors and the central nitrogen donor and a "tetrahedral π-imine compartment" consisting of the other pyridine and an "imine C═N" donor. The formation of an "imine donor" in this process is the result of substantial electron transfer from the {bpa-2H}(2-) ligand to one of the rhodium centers to form the neutral imine ligand bpi (bpi = PyCH(2)N═CHPy).

Ligand-centred reactivity of bis(picolyl)amine iridium: sequential deprotonation, oxidation and oxygenation of a "non-innocent" ligand.

Treatment of [Ir(bpa)(cod)](+) complex [1](+) with a strong base (e.g., tBuO(-)) led to unexpected double deprotonation to form the anionic [Ir(bpa-2H)(cod)](-) species [3](-), via the mono-deprotonated neutral amido complex [Ir(bpa-H)(cod)] as an isolable intermediate.

Intervalent bis(mu-aziridinato)M(II)--M(I) complexes (M=Rh,Ir): delocalized metallo-radicals or delocalized aminyl radicals?

Reactions of the methoxo complexes [{M(mu-OMe)(cod)}(2)] (cod=1,5-cyclooctadiene, M=Rh, Ir) with 2,2-dimethylaziridine (Haz) give the mixed-bridged complexes [{M(2)(mu-az)(mu-OMe)(cod)(2)}] [(M=Rh, 1; M=Ir, 2). These compounds are isolated intermediates in the stereospecific synthesis of the amido-bridged complexes [{M(mu-az)(cod)}(2)] (M=Rh, 3; M=Ir, 4). The electrochemical behavior of 3 and 4 in CH(2)Cl(2) and CH(3)CN is greatly influenced by the solvent.

Formation of a bridging-imido d6 rhodium compound by nitrene capture. insertion and cycloaddition reactions.

The first d (6) rhodium imido complex, [{(C 5Me 5)Rh(mu-NSO 2C 6H 4Me- p)} 2] ( 2), has been obtained from the reaction of [(C 5Me 5)Rh(C 2H 4) 2] with chloramine-T. Carbon monoxide inserts into the N-Rh bonds in 2 to give the dinuclear ureylene complex [(C 5Me 5)Rh(mu-{(Ts) N-CO-N(Ts)}Rh(CO)(C 5Me 5)], while the azide C 6F 5N 3 adds to 2 to give the mononuclear tetrazene complex [(C 5Me 5)Rh{( p-MeC 6H 4SO 2)N 4(C 6F 5)}].

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].