Polynuclear Rhodium Complexes with Dinucleating PNNP Ligand:  Dynamic and Diverse M···M Interactions in [(μ-X)Rh₂(PNNP)(CO)₂]ⁿ⁺and [(μ₄-X)Rh₄(PNNP)₂(CO)₄]ⁿ⁺[X = H, O, C⋮C−R, R−C⋮C−R, C⋮C, CHCH₂, SMe₂;n= 0, 1:  PNNP = 3,5-bis(diphenylphosphinomethyl)pyrazolato]

Abstract

The dirhodium-tetracarbonyl complex with the PNNP ligand, [Rh 2 (PNNP)(CO) 4 ]BF 4 , 1‚BF 4 [PNNP ) 3,5-bis(diphenylphosphinomethyl)pyrazolato], serves as a precursor for the active species [Rh 2 (PNNP)(CO) 2 ] + , A, with cis-divacant coordination sites, which can accommodate a donor species with up to four donor electrons. Interaction of 1‚BF 4 with LiCtC-R, Li-CHdCH 2 , PPN[M(CO) n ], CN-Cy, SMe 2 , and Et-CtC-Et leads to the formation of the corresponding dinuclear adducts [(X)Rh 2 (PNNP)(CO) 2 ] n+ (BF 4 ) n [X/n ) µ-η 1 :η 2 -CtC-R/0 (2), µ-η 1 :η 2 -CHdCH 2 /0 (3), µ-Co(CO) 4 /0 (4a), µ-Mn(CO) 5 /0 (4b), (η 1 -CtN-Cy) 2 /1 (5‚BF 4 ), µ-η 1 :η 1 -SMe 2 /1 (6‚BF 4 ), µ-η 2 :η 2 -Et-CtC-Et/1 (7‚BF 4 )], respectively. Selective replacement of the inner CO ligands trans to the P atoms is verified by spectroscopic and crystallographic characterizations of the adducts. The µ-acetylide (2) and µ-vinyl complexes (3) show dynamic behavior via the conventional windshield wiper motion of the unsaturated hydrocarbyl ligand. Systematic structural analysis of a series of the µ-acetylide complexes 2 (R ) H, SiMe 3 , n-Bu, Ph, p-tol) reveals three typical conformations for the Rh 2 (PNNP)(CO) 2 backbone: C s -(type I), C 2 -(type II), and C 2v -symmetrical ones (type III). On the other hand, interaction of 1‚BF 4 with 1-alkyne, hydrosilanes, and hydroxo anion produces tetranuclear adducts resulting from 1 (donor):2 [Rh 2 (PNNP)(CO) 2 ] coupling reactions. The µ 4 -η 1 (C R ):η 2 (C R tC )-acetylide complexes, [(µ 4 -CtC-R)Rh 4 (PNNP) 2 (CO) 4 ]BF 4 , 8‚BF 4 , consisting of an acyclic, folded Z-shaped Rh 4 linkage are fluxional via a combination of windshield wiper-like motions between the wingtip Rh centers and between the wingtip and hinge Rh centers, which involve reversible M-M bond scission and recombination processes. The ethynyl complex 8a‚BF 4 (R ) H) is readily deprotonated by the action of a base to give the µ 4 -dicarbide complex (µ-η 1 :η 1 :η 2 :η 2 -CtC)Rh 4 (PNNP)(CO) 4 , 9, via cleavage of three Rh-Rh bonds, and this process is reversed upon protonation of 9 with HBF 4 . The reaction of 1‚BF 4 with hydrosilanes and hydroxo anion furnishes the isostructural tetranuclear complexes [(µ 4 -X)Rh 4 (PNNP)(CO) 4 ] n+ -(BF 4 ) n [X/n ) H/1 (10‚BF 4 ), O/0 (11)], in which the four Rh atoms arranged in a tetrahedral array are connected by the µ 4 -bridging ligand (X), as characterized by X-ray crystallography. The tetranuclear structures are retained mainly by Rh-X interactions even in the case of the electron-deficient hydride complex 10‚BF 4 with 58 valence electrons (cf. 64e for a coordinatively saturated species), where the filled, spherically distributed 1s orbital of the hydride ligand interacts with the four Rh centers arranged in a tetrahedral array. Depending on the size of the bridging ligand X, the structure of the tetranuclear complexes varies from the encapsulated structure (10‚BF 4 and 11) to the one with a folded Z-shaped metal linkage (8‚BF 4 ). The present study reveals (i) the high reactivity (electr...

Mechanistic Investigation on the Polymerization of Phenylacetylene by 2-Diphenylphosphinopyridine Rhodium(I) Catalysts: Understanding the Role of the Cocatalyst and Alkynyl Intermediates

“…Notably the intermetallic distance [Rh(1)···Rh(2) 3.1361(7)] rules out any metal–metal interaction [rhodium covalent radius 1.42(7) Å] and the dinuclear frame is exclusively supported by the 1κ P ,2κ N -Ph 2 PPy and the 1κ C ,2κ 2 C,C′ -CCPh ligands. To the best of our knowledge, only very few dinuclear rhodium­(I) complexes featuring a 1κ P ,2κ N coordination mode of Ph 2 PPy have been structurally characterized so far, all of them containing a μ-CO ligand and featuring intermetallic distances indicative of a metal–metal interaction (<2.70 Å). − On the other hand, the 1κ C ,2κ C,C′ coordination mode of acetylides is quite common, and as for rhodium­(I) dinuclear complexes, several derivatives containing the Rh 2 (1κ C ,2κ 2 C,C′ -CCR) motif have already been reported nicely featuring rhodium–carbon bond lengths similar to those observed in 12 . − …”

Noble metals

“…124 Finally, the polynuclear rhodium complexes with the dinucleating ligand 3,5-bis(diphenylphosphinomethyl)pyrazolate (L), have been shown to have dynamic and diverse Rh-Rh interactions in the complex [(m-X)Rh 2 (L)(CO) 2 ] n1 and [(m 4 -X)Rh 4 (L) 2 (CO) 4 ] z1 [X = H, O, CRC-R, R-CRC-R, HCRCH, CHQCH 2 , SMe 2 ; z = 0, 1; R = Et and Cy], revealing that M-M bonds are not always essential for a polynuclear system, but can be controlled by the electrophilicity of the ligands. 125…”

Multidentate Pyridyl‐Aminophosphinite and Pyridyl‐Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre‐Catalysts

“…The design of multidentate ligands containing mixed‐donor atoms to functionalize transition metal centers is a subject of growing interest in coordination and organometallic chemistry Multidentate mixed‐donor ligands function cooperatively in stabilizing metal centers due to their different binding abilities and bridging effect between two or more metal centers . These synergistic effects are helpful in making complexes containing multidentate mixed‐donor ligands very attractive for several applications including catalysis . Catalytic activity of these ligands also results from easy dissociation of the weakly coordinated donor atoms to create vacant site for the incoming substrate.…”