Phosphine Fragment Research Articles

Formation of a chiral NPPN ligand via metallation of acyclic NPNCN systems

A new type of bidentate N,N'-chelating ligand containing a chiral phosphorus centre has been synthesized via the metallation of an acyclic NPNCN species. The zwitterionic ligand backbone contains a phosphenium centre stabilised by an imido phosphine fragment.

10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin as a building block for porphyrin coordination arrays

10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin, ( SDPyDTP ) H , was prepared by condensation of 2,5-bis(4-tolylhydroxymethyl)thiophene, pyrrole and 4-pyridinecarboxaldehyde in boiling propionic acid. The synthesis introduced two pyridyl substituents at two defined (opposite to thiophene) meso positions of the porphyrin periphery. The self-assembly of the angular 10,15-dipyridyl-21-thiaporphyrin modules with cis square-planar diphosphineplatinum(II) complex leads to a cyclic rhomboid dimer [ Pt ( DPPP )( SDPyDTP ) H ]2( OTf )4. The molecule acquires butterfly geometry. The 1 H NMR studies confirmed the π-π stacking of the pyridyl ring with the equatorial phenyl rings of the phosphine fragment. The conformational equilibrium, interchanging the phenyl ring positions and affording the mixture of seven conformers in solution, has been considered. 1 H NMR> spectroscopy was applied to identify oligomeric species, constructed by coordination of ( SDPyDTP ) H to the paramagnetic nickel(II) complex 5,10,15,20-tetra(4-tolyl)-21-thiaporphyrin, ( STTP ) Ni II Cl . ( SDPyDTP ) H acts as a mono- or bidentate ligand coordinating by meso-pyridyl substituents. Using the paramagnetically shifted resonances as an unambiguous spectroscopic probe, 1 H NMR spectroscopy readily discriminated between five- {[( STTP ) Ni II ](( SDPyDTP ) H )} and six-coordinate {[( STTP ) Ni II](( SDPyDTP ) H )2} oligomeric subunits. The applicability of 10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin as a suitable building block in construction of larger molecules was confirmed. The new route to modify the porphyrin coordination arrays, which preserves the overall architecture but modifies intrinsic chemical properties, using heteroporphyrin was demonstrated.

Electronic Differences between Coordinating Functionalities of Chiral Phosphine−Phosphites and Effects in Catalytic Enantioselective Hydrogenation

A convenient synthesis of new chiral phosphine−phosphites (P−OP) has been described. The versatility of the synthetic protocol developed has allowed the preparation of ligands with different phosphine fragments and the choice of the stereogenic element location. Analyses of the values of 1JPSe of the corresponding diselenides are in accord with the expected lower σ-donor ability of the phosphite fragment, with respect to the phosphine group, and with an increase of phosphine basicity after substitution of phenyl substituents by methyl groups. Inspection of υ(CO) values on a series of complexes RhCl(CO)(P−OP) demonstrated a variable π-aceptor ability of the phosphite group, compensating for the change of basicity of the phosphine functionality, as well as having a rather reduced electron density at the metal center compared with diphosphine analogues. The distinct nature of the phosphorus functionalities has also been evidenced in rhodium-catalyzed enantioselective hydrogenation of methyl Z-α-acetamido-cinnamate (MAC). Thus, the coordination mode of the substrate is governed by the chiral ligand, directing the olefinic bond to a cis position with respect to the phosphite group, as demonstrated by NMR studies performed with [Rh(P−OP)(MAC)]+ complexes. In consequence, the phosphite group has a greater impact on the enantioselectivity of the product. However, the optical purity of the process also depends on the nature of the phosphine group, and hence, an appropriate election of both phosphorus functionalities is required for the attainment of excellent enantioselectivities (99% ee).

Optically active cyclopalladated compounds containing P-chiral ligands. Restricted rotation around the PdP bond

The synthesis of the optically active complexes [PdCl(C 10H 6CHMeNMe 2)L] (L=PPh 3, PBn 2Ph, PHBnPh and PBnCyPh) and the resolution of the secondary phosphine PHBnPh is reported. The study of the NMR data of these mononuclear compounds shows that in some of these complexes the rotation around the PdP bond is restricted. A relationship between the δ values of the aromatic proton adjacent to the PdC bond and the conformation of the Pd–phosphine fragment can be found and NMR data permit the assignment of the absolute configuration of the phosphine in [PdCl(C 10H 6CHMeNMe 2)(PBnCyPh)]. Several molecular mechanics geometry optimizations were performed using the MMFF94 force field to estimate the height of the energy barrier corresponding to the rotation of the phosphine ligands around the PdP bond. These calculations show the rotation around the PdP bond to be restricted, if the phosphine contains at least one benzylic group, and agree with the results obtained in solution by means of mono- and bi-dimensional NMR.

Trigold(I) Phosphine Derivatives of Clusters Containing Octahedral Rh2Ru4B-Boride Cores: The X-Ray Structure of [Rh2Ru4(CO)15Rh2Ru4B{AuPCy3}3] (Cy = cyclohexyl)

The reaction of [Rh(CO)2Cl]2 with [HRu4(CO)12BH]- followed by treatment with an excess (at least three-fold) of [Cy3PAuCl] (Cy = cyclohexyl) leads to the formation of [Rh2Ru4(CO)16B{AuPCy3}] (previously prepared by another route) and [Rh2Ru4(CO)15B{AuPCy3}3]. The new trigold derivative has been characterized by spectroscopic and mass spectrometric methods, and by single crystal X-ray diffraction. It possesses an octahedral Rh2Ru4 core containing an interstitial boron atom; two of the gold(I) phosphine units cap two adjacent faces and the third bridges an edge of the octahedral cage. There are no close Au···Au contacts. Reactions of [Rh2Ru4(CO)16B]- with [(R3PAu)3O]+ (R = Ph, 2-MeC6H4) resulted in the formation of [Rh2Ru4(CO)15B{AuPR3}3]; for R = Ph, two isomers in respect of the arrangements of the AuPPh3 were isolated. Fluxional processes involving the gold(I) phosphine fragments have been observed using solution variable-temperature 31P NMR spectroscopy.

Transition Metal Substituted Acylphosphines and Phosphaalkenes. 25. Unprecedented Condensation of the Pentamethylcyclopentadienyl Ligand with a Methylene Phosphine Moiety in (.eta.5-C5Me5)(CO)2FeP:C(NMe2)2 Induced by Azodicarboxylates. Structure of [cyclic] .eta.5-C5Me4CH:C(NMe2)PN(CO2CMe3)NH(CO2CMe3)Fe(CO)2

The metallophosphaalkene (h5-C5Me5)(CO)2FeP:C(NMe2)2 (I) undergoes reaction with dialkyl azodicarboxylates RO2CN:NCO2R (R = CMe3, Et, CH2Ph) to afford complexes II (R = CMe3, Et, CH2Ph) with the novel chelating 3-(tetramethylcyclopentadienyl)-1-phospha-2-propenyl ligand. This ligand system results from a yet unprecedented azocarboxylate-induced condensation of a ring Me substituent with the methylene phosphine fragment of educt I. The mol. structure of II (R = CH2Ph) (P21/c, a = 10.522(3) .ANG., b = 22.124(9) .ANG., c = 12.806(4) .ANG., b = 101.58(3) Deg) was detd. by single-crystal x-ray anal.

Heterometallic boride clusters: formation of octahedral [M2Ru4(CO)16B]–(M = Rh or Ir) and gold(I) phosphine derivatives. Crystal structures of [N(PPh3)2][trans-Ir2Ru4(CO)16B], trans-[Rh2Ru4(CO)16B{µ3-AuP(C6H11)3}] and cis-[Ir2Ru4(CO)16B{µ-AuP(C6H11)3}

The reaction of the butterfly cluster [Ru4H(CO)12BH]– with [Rh2(CO)4Cl2] led to the octahedral boride [Rh2Ru4(CO)16B]–1. In solution, 11B NMR spectroscopic evidence supports the presence of both cis- and trans-isomers of 1. The trans form is predominant. When treated with [AuCl{P(C6H11)3}], 1 yielded [Rh2Ru4(CO)16B{AuP(C6H11)3}]3 in two isomeric forms 3a and 3b. Similar reactions occur with other phosphine gold(I) derivatives. The crystal structure of compound 3a has been determined and reveals a trans arrangement of Rh atoms and a face capping AuP(C6H11)3 unit. The anion [Ru4H(CO)12BH]– reacted with [Ir2L4Cl2](L = cycloctene or L2= cycloocta-1,5-diene) under a stream of CO to give [Ir2Ru4(CO)16B]–2; the crystal structure of 2 has been determined and confirms an octahedral metal framework with trans iridium atoms. Cluster 2 reacted with [AuCl{P(C6H11)3}] to yield [Ir2Ru4(CO)16B{AuP(C6H11)3}]4 and crystallographic data for 4 show that the Ir atoms are mutually cis in the octahedral Ir2Ru4 skeleton. The AuP(C6H11)3 unit bridges the Ir–Ir edge. In [Ru4H(CO)12BH]–, the four ruthenium atoms define a butterfly framework with the boron atom lying in a semi-interstitial position. The addition of two Group 9 metal atoms to close up the metal cage to an octahedral one with an M2Ru4 core should initially give a cis isomer. In fact the trans isomer is observed for both 1 and 2, although for 1 both cis and trans isomers are observed by 11B NMR spectroscopy. Geometrical preferences which accompany the addition of a gold(I) phosphine fragment to anions 1 and 2 to give 3 and 4 respectively are discussed.

P-Funktionalisierte diferriophosphonium salze des typs [{CpFe(CO) 2} 2PPhR] +X- und [{CpFe(CO) 2 } 2PClR] +X-

Diferriophosphonium salts containing an alkyl-substituent can be synthesised by two different ways. The first is the deprotonation of [{CpFe(CO) 2} 2PPhH]Cl ( 1) with KO tBu in THF as a one-pot reaction at −78°C to give the unstable diferriophosphine complex {CpFe(CO) 2} 2PPh ( 2) and its realkylation by RX (R = Me, CH 2Ph, CH 2COOEt; X = Cl, I), which results in the open diferriophenylalkylphosphonium salts [{CpFe(CO) 2} 2PPhR]X ( 3a–c). Photolysis of 3a-c eliminates one CO-group with formation of the closed diferriophosphonium salts 4a-c with one bridging CO ligand and a FeFe bond. Deprotonation of the salts 3a,b by bases gives the unstable neutral diferriophenylphosphorus-ylides or better the η 2-phosphaalkene complexes (CpFe(CO) 2 2PPhCHR′ ( 5a,b), which eliminate the dimer [CpFe(CO) 2] 2 to finally give the 1,3-diphosphetanes (PhPCHR′) 2 by dimerisation of the unstable phosphaalkene. The second and much easier method for the preparation of diferrioalkylphosphonium salts is the cleavage reaction of [CpFe(CO) 2] 2 with RPCl 2 in toluene. The phosphine fragment RPCl inserts into the FeFe bond to give the chlorine substituted diferriophosphonium salts [{CpFe(CO) 2} 2PClR]Cl (R = Ph, Me, 1Pr, Cl) ( 6d–g) and [{CpFe(CO) 2} 2PMesH]Cl ( 7). The mass, IR and NMR spectra of 3, 4, 6 and 7 and the reactivity of the compounds 3a-c, as well as the results of the X-ray structure analysis of the first mixed alkyl-aryl- diferriophosphonium salt [{CpFe(CO) 2} 2PPhCH 2Ph]BPh 4 ( 3b′), are reported and discussed.