Bidentate Nitrogen Donor Ligands Research Articles

2‐Thiopheneacetato‐Based One‐Dimensional Coordination Polymer of Tb3+: Enhancement of Terbium‐Centered Luminescence in the Presence of Bidentate Nitrogen Donor Ligands

AbstractFour new lanthanide(III) complexes of 2‐thiopheneacetic acid (HTPAC), [Tb(TPAC)3·H2O]n (1), [Gd(TPAC)3·H2O]n (2), [Tb(TPAC)3(phen)]2 (3) and [Tb(TPAC)3(bath)]2 (4) (phen = 1,10‐phenanthroline; bath = bathophenanthroline) have been synthesized and characterized by various spectroscopic techniques. The X‐ray structure of 1 reveals that each Tb3+ ion is connected to two neighboring ions by six thiopheneacetic acid ligands via the carboxylate groups to form an infinite one‐dimensional polymer. The unit cell contains only one independent crystallographic site for the Tb ions. The carboxylate groups of the six molecules of the thiopheneacetate ligands are coordinated in both bidentate bridging and tridentate chelate‐bridging modes. Each Tb3+ ion is coordinated by nine oxygen atoms in an overall distorted tricapped trigonal‐prismatic geometry. Eight of the oxygen atoms are furnished by the carboxylate moieties, and the remaining oxygen atom is provided by the water molecule. The photophysical properties of these complexes in the solid state at room temperature have been investigated. The quantum yields of 3 (4.43 ± 0.44 %) and 4 (9.06 ± 0.90 %) were found to be significantly enhanced by the presence of the bidentate nitrogen donor ligands in comparison with that of 1 (0.07 ± 0.01 %) due to effective energy transfer from the secondary ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Ethylene Dimerization by Cationic Palladium(II) Alkyl Complexes that Contain Bis(heterocycle)methane Ligands

The catalytic ethylene dimerization reactions of (N∧N)PdMe(L)+ species that contain bidentate nitrogen donor ligands were studied (N∧N = (1-Me-imidazol-2-yl)2CH2 (a); (1-Me-imidazol-2-yl)2CH(C6H13) (b), 1,1′-di(triphenylmethyl)-4,4′-biimidazole (c), (5-Me-pyridin-2-yl)2CH2 (d), (pyrazol-1-yl)2CH2 (e), (3,5-Me2-pyrazol-1-yl)2CH2 (f), (4-Me-C6H4)N═CMeCMe═N(4-Me-C6H4) (g), and (2,6-iPr2-C6H3)N═CMeCMe═N(2,6-iPr2-C6H3) (h)). (N∧N)PdMe2 (2a–e,g) and (N∧N)Pd(Me)Cl (3f–h) complexes were converted to [(N∧N)Pd{C(═O)Me}CO][B(C6F5)4)] (7a,c–h), [(N∧N)Pd(Me)(H2C═CH2)][B(C6F5)4)] (8a−g), and [(N∧N)Pd(Me)(H2C═CH2)][SbF6] (8f′). The νCO values for 7a,c−f show that there is weak back-bonding in these species, the donor ability of the N∧N ligand varies in the order imidazole > pyridine > pyrazole, and variation of the chelate ring size does not strongly affect the electron density at Pd. 8a,c−g and 8f′ dimerize ethylene by an insertion/β-H elimination mechanism. The catalyst resting state is (N∧N)Pd(Et)(H2C═CH2)+ (9a,c−g). First-order rate constants for ethylene insertion of 8a−g and 8f′ (kinsert,Me) and 9a,c−g (kinsert,Et) were determined by NMR. The kinsert,Me and kinsert,Et values for analogous (N∧N)Pd(R)(H2C═CH2)+ species are similar. Increasing the electrophilic character and the steric bulk of the (N∧N)Pd unit leads to moderate increases in ethylene insertion rates.

Synthesis of new palladium(II) compounds with several bidentate nitrogen-donor ligands: Structural analyses by 1H and 13C{ 1H} NMR spectroscopy and crystal structures

The reaction of [PdCl 2(CH 3CN) 2] with N-alkylaminopyrazole ( NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole ( deae), 1-[2-( i propylamino)ethyl]-3,5-dimethylpyrazole ( deai), and 1-[2-( t butylamino)ethyl]-3,5-dimethylpyrazole ( deat), affords a series of square planar Pd(II) complexes [PdCl 2( NN′)] ( NN′ = deae ( 1), deai ( 2) and deat ( 3)). The solid-state structures of complexes 1 and 3 were determined by single crystal X-ray diffraction studies. The NN′ ligands are coordinated through the N pz and N amine atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, 1H and 13C{ 1H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.

New cationic palladium(II) compounds with several bidentate nitrogen-donor ligands: Synthesis, spectroscopic analyses and X-ray crystal structure

A series of PdN 4 core complexes has been synthesised. Reaction of [PdCl 2(CH 3CN) 2] with N-alkylaminopyrazole ( NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole ( deae), 1-[2-( i propylamino)ethyl]-3,5-dimethylpyrazole ( deai), and 1-[2-( t butylamino)ethyl]-3,5-dimethylpyrazole ( deat) in the presence of AgBF 4 led to [Pd( NN′) 2](BF 4) 2. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, 1H and 13C{ 1H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed. The X-ray analyses of one representative complex, [Pd( deat) 2](BF 4) 2, is reported. The crystal structure consists of discrete centrosymmetric cations involving a coordinated Pd(N pz) 2(N amino) 2 core with planar geometry and BF 4 - anions.

Intramolecular Hydroamination Catalyzed by Cationic Rhodium and Iridium Complexes with Bidentate Nitrogen-Donor Ligands

Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N−N)(CO)2]+[X]-, incorporating the bidentate heterocyclic nitrogen donor ligands (N−N) bis(1-methylimidazol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm), are efficient catalysts for hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding five-membered imine heterocycle was achieved in good yield with excellent regioselectivity using both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts has a significant effect on the rate of the hydroamination reaction and interionic contacts between the metal complexes and their counterions in solution were clearly visible by NMR spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction in solution. The nature of the coligands also had a significant effect on the efficiency of the metal complexes as catalysts, and complexes containing phosphine coligands were less effective catalysts compared to those complexes containing CO coligands. The X-ray crystal structure of the new iridium(I) complex [Ir(bim)(CO)2]+[BPh4]- (2) is reported, as well as the synthesis and characterization of the Rh complex [Rh(bpm)(CO)2]+[BPh4]- (3).

Peripherally Metallated Porphyrins: the First Examples of meso‐η1‐Palladio(II) and ‐Platinio(II) Complexes with Chelating Diamine Ligands

AbstractThe oxidative addition of bis(dibenzylideneacetone)platinum(0) to meso‐bromo‐5,15‐diarylporphyrins in the presence of PPh3 has been shown to be an effective way of synthesising η1‐organoplatinum porphyrins in high yields. This methodology has been extended to synthesise various palladio‐ and platinioporphyrins that utilise bidentate nitrogen donor ligands [N,N,N′,N′‐tetramethylethylenediamine (tmeda) and 2,2′‐bipyridyl (bpy)] in order to enforce a cis configuration at the metal centre. The products were characterised by multinuclear NMR and UV‐Vis spectroscopy as well as fast‐atom bombardment and high‐resolution electrospray ionisation mass spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Carbon−Oxygen Bond Formation at Organopalladium Centers: The Reactions of PdMeR(L2) (R = Me, 4-tolyl; L2 = tmeda, bpy) with Diaroyl Peroxides and the Involvement of Organopalladium(IV) Species

The group 16 oxidants dibenzoyl- and bis(4-trifluoromethylbenzoyl)-peroxide react with dimethylpalladium(II) and methyl(4-tolyl)palladium(II) complexes of the bidentate nitrogen donor ligands 2,2'-bipyridine and N,N,N'N'-tetramethylethylenediamine in discrete stepwise processes as the temperature is raised from -70 °C. Carbon-oxygen bonds are formed during this reaction sequence but not from those Pd(IV) complexes detected spectroscopically. The initial reaction gives undetected “PdIV(O2CAr)2MeR(L2)” (Ar = Ph, ArF; R = Me, Tol; L2 = bpy, tmeda), which immediately undergo methyl aroate exchange with PdIIMeR(L2) to give PdII(O2CAr)R(L2) and PdIV(O2CAr)Me2R(L2), where all products except for PdIV(O2CAr)Me2- Tol(tmeda) were detected by 1H NMR spectroscopy. On raising the temperature, the PdIVMe3 complexes reductively eliminate Me-Me, and the PdIVMe2Tol complexes eliminate Me- Me and Tol-Me. The resultant Pd(II) complexes PdII(O2CAr)R(L2) react with (ArCO2)2 at higher temperatures to form PdII(O2CAr)2(L2) and R-O2CAr (R = Me, Tol), except for PdII(O2- CAr)Tol(tmeda), which forms PdII(O2CAr)2(tmeda) and 4,4'-bitolyl. Each reaction step has been confirmed by the independent synthesis of intermediates PdII(O2CAr)2(L2) and PdII(O2- CAr)R(L2) (Ar =Ph, ArF; R=Me, Tol; L2 = bpy, tmeda) and PdIV(O2CR)Me2R(L2) (R = Ph, ArF; R= Me, Tol; L2 = bpy) by metathesis reactions of halogeno complexes with Ag[O2CAr], followed by temperature-dependent studies of both the decomposition of Pd(IV) complexes and reactions of Pd(II) complexes with (ArCO2)2. Attempts to prepare “PdIV(O2CAr)2MeR- (bpy)” in a similar manner (and thus in the absence of PdMeR(bpy) with which they undergo exchange reactions) were unsuccessful, but the complexes PdIVI2MeR(bpy) (R=) Me, Tol) that formed on reaction of diiodine with PdMeR(L2) were detected and found to reductively eliminate iodomethane. X-ray structural studies are reported for the square-planar palladium( II) complexes Pd(O2CPh)2(bpy), Pd(O2CAr)2(tmeda) (Ar = Ph, ArF), and Pd(O2CPh)-

Cationic palladium complexes with mono- and bidentate nitrogen-donor ligands: synthesis, characterization and reactivity in CO/styrene copolymerization reaction

Two series of cationic palladium(II) complexes, [Pd(phen)(L) 2][PF 6] 2 (L=pyridine ( 1a), 2-picoline (2-pic) ( 1b), 3-picoline (3-pic) ( 1c), 4-picoline (4-pic) ( 1d)) and [Pd(CH 3)(L)(phen)][OTf] (L=2-pic ( 2b), 3-pic ( 2c) and 4-pic ( 2d)), with mono and bidentate nitrogen-donor ligands bound to the same metal center have been synthesized and characterized. For the dicationic derivatives the study of the chemical behavior in solution evidences the presence of restricted rotations around the PdN bond of the monodentate ligand, generating syn and anti isomers. Depending on the nature of L the rate of this dynamic process is different on the NMR time scale. On the other hand, only the syn isomer was found by the X-ray analysis in solid state of one of these complexes. The dicationic complexes have been tested as precatalysts in the CO/styrene copolymerization, in comparison with [Pd(phen) 2][PF 6] 2. The main difference between the two kinds of precatalysts is related to the stability of the corresponding active species, being lower for the complexes [Pd(phen)(L) 2][PF 6] 2 than for the bischelated derivative. The insertion reaction of carbon monoxide in the Pdmethyl bond was studied on the monocationic complexes, [Pd(CH 3)(L)(phen)][OTf]. In all cases the corresponding Pdacyl species [Pd(COCH 3)(L)(phen)][OTf] was formed with no dissociation of the monodentate L ligand. No effect of the nature of L on the rate of the insertion reaction was evidenced.

A new class of ferromagnetically-coupled mixed valence vanadium(IV/V) polyoxometalates.

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).

Attractive ligand–ligand interactions involving aromatic rings in five-coordinate ternary copper(II) complexes with a dipeptide and a bidentate N-donor ligand

Structures and stabilities of ternary copper(II) complexes, Cu(DP)(DA), where DP and DA denote dipeptides with an aromatic amino acid residue and bidentate nitrogen donor ligands, respectively, have been studied by synthetic, crystallographic, potentiometric, and spectroscopic methods. The X-ray crystal structure analysis of [Cu(gly·l-tyr)(bzp)] (gly·l-tyr=glycyl-l-tyrosinate, bzp=N-benzyl-N-2-pyridylmethylamine) revealed that the complex has a distorted square-pyramidal structure exhibiting an intramolecular edge-to-face stacking interaction between the pyridine ring of bzp and the phenol ring of gly·l-tyr around the Cu(II) center. [Cu(gly·l-tyr)(bzmp)] (bzmp=N-benzyl-N-6-methyl-2-pyridylmethylamine) was also revealed to have a similar structure and an intramolecular CH-π-type interaction between the methyl group of bzmp and the phenol ring of gly·l-tyr. The absorption spectra of the ternary Cu(II)–DP–DA systems in water showed that the ternary complexes have a shoulder peak near 900 nm, supporting that the Cu(II) center has a square-pyramidal geometry. From the stability constants for the ternary Cu(II) complexes determined by pH titration at 25°C and I=0.1 M (KNO3), Cu(gly·l-tyr)(DA) and Cu(gly·l-trp)(DA) (DA=ligands with one or two aromatic rings) were found to be stabilized relative to Cu(gly·gly)(DA) (gly·gly=glycylglycinate), which has been concluded to be due to the contribution of the edge-to-face or CH-π interactions within the complexes in solution.

New monocationic methylpalladium(II) compounds with several bidentate nitrogen-donor ligands: synthesis, characterisation and reactivity with CO

Two series of methylpalladium(II) compounds with mono and bidentate nitrogen-donor ligands, namely [Pd(N-N) 2(CH 3)][X] (N-N=phen ( 1a), dm-phen ( 1b) (dm-phen=4,7-dimethyl-1,10-phenanthroline), tm-phen 1c (tm-phen=3,4,7,8-tetramethyl-1,10-phenanthroline); X=OTf, PF 6 − ) and [Pd(N-N)(L)(CH 3)][OTf] (N-N=phen and L=py ( 1ad) (py=pyridine), N-N=phen and L=2-Ph-py ( 1ae) (2-Ph-py=2-phenyl-pyridine), N-N=phen and L=BzQ ( 1af) (BzQ=7,8-benzoquinoline), N-N=tm-phen and L=BzQ ( 1cf)), have been synthesised and fully characterised both in solid state and in solution. The crystal structures of [Pd(phen) 2(CH 3)][PF 6] and [Pd(phen)(2-Ph-py)(CH 3)][OTf] show a square planar coordination geometry for palladium with the monodentate ligand (one phen molecule plays this role in 1a) bound to the metal with its plane almost perpendicular to the coordination plane. In both structures the PdN bond length trans to the methyl is remarkably affected by its trans influence. The behaviour in solution is characterised for the first series of compounds by a dynamic process which makes the two N-N ligands equivalent, as corroborated by the 15N NMR analysis: only one averaged signal is shown for all of the four nitrogen atoms. No fluxional process is present for the compounds of the second series, and three main crosspeaks are shown in the 15N– 1H HMQC spectra. In particular, the signal of the 15N trans to the methyl group has a typical chemical shift, which differs from those of two 15N trans to each other. Both series of complexes are reacted with carbon monoxide and the reaction products are studied by 1H NMR spectroscopy and, when possible, by isolating the acyl derivatives. The products of this reaction are affected by the nature of the second molecule of N-ligand.

(Dimethyl)dioxomolybdenum(VI) complexes: syntheses and catalytic applications

Reaction of MoO 2Br 2S 2 complexes [S=THF, CH 3CN] with bidentate nitrogen donor ligands (L 2) leads to complexes of the type MoO 2Br 2L 2 in good yields, L 2=substituted bipyridylphenantroline, 1,4-R 2-diazabutadiene and bipyrimidine. Treatment of the latter complexes with Grignard reagents at low temperatures yields complexes of the general formula MoO 2(CH 3) 2L 2 and MoO 2(C 2H 5) 2(diphenylphenantroline). 1H NMR and IR data are comparatively indifferent to the ligand changes. The 95Mo NMR data of selected complexes reflect the donor capability of the organic ligands. Mass spectroscopy and temperature-dependent 95Mo NMR spectroscopy show a significant stability of the MoN bond. The compound MoO 2(CH 3) 2(bipyrimidine) was additionally examined by single crystal X-ray analysis. The catalytic activity of the MoO 2R 2L 2 complexes in olefin epoxidation with t-butyl hydroperoxide as oxidizing agent is strongly influenced by the nature of the ligand L and its steric bulk in the equatorial plane. The title complexes with a Mo(CH 3) 2 moiety are slightly less active in catalysis than the MoBr 2 precursor compounds. Increase of both reaction time and/or temperature lead to a significant increase in the product yield in all examined cases. At about 90°C catalyst decomposition hampers further product yield increase.

A Novel Noninterpenetrating Polycyclohexane Network: A New Inorganic/Organic Coordination Polymer Structural Motif Generated by Self-Assembly of “T-Shaped” Moieties

The new bidentate nitrogen-donor ligand 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (4) has been synthesized (monoclinic, P21/c, a = 11.074(2) A, b = 4.737(1) A, c = 11.475(2) A, β = 115.861(9)°, V = 541.7(1) A3, Z = 4) and its coordination chemistry with cadmium and cobalt nitrate hydrates investigated. Two new noninterpenetrating coordination polymers based on “T-shaped” building blocks have been obtained: [Cd(NO3)2(C12H10N4)1.5·CH2Cl2]n (5) (monoclinic, P21/n, a = 7.891(1) A, b = 17.172(3) A, c = 18.576(4) A, β = 97.72(1)°, V = 2494.5(7) A3, Z = 4) and [Co(NO3)2(C12H10N4)1.5·CH2Cl2]n (6) (monoclinic, P21/n, a = 7.7954(8) A, b = 17.026(3) A, c = 18.412(3) A, β = 97.89(1)°, V = 2420.6(6) A3, Z = 4). Both 5 and 6 adopt a novel “polycyclohexane” structural motif, consisting of “all-equatorially” condensed cyclohexane-like M6(ligand)6 units. They are open-framework materials with unusually large cavities (ca. 28 × 15 A), and reversibly absorb and desorb guest molecules between room temperature and 213 °C wi...

Lewis base adducts of bis-(halogeno)dioxomolybdenum(VI): syntheses, structures, and catalytic applications

Reaction of solvent substituted MoO 2X 2(Solv) 2 complexes ((Solv)=THF, CH 3CN) with mono- and bidentate nitrogen and oxygen donor ligands leads to complexes of the type MoO 2X 2L 2 in nearly quantitative yields at room temperature within a few minutes. The 95 Mo and 17 O NMR data of selected complexes as well as the MoO IR vibrations were used to probe the influence of the ligands on the electronic properties of the metal and the MoO bond. Two complexes have additionally been examined by single crystal X-ray analysis. The activity of the MoO 2X 2L 2 complexes as catalysts in olefin epoxidation with t-butylhydroperoxide as oxidizing agent depends on both the nature of the organic ligand L and the halogeno ligand X. The difference in activity observed between Cl and Br substituted complexes is not very pronounced. In general, the Cl derivatives are more active than their Br analogues. The organic ligands L display a significant influence on the catalytic performance. Complexes with ligands bearing aromatic substituents at N are in all cases, much more active than those bearing aliphatic substituents. The less active complexes can be activated by raising the temperature and extending the reaction time. In all observed cases, these changes produce a significant increase of the product yield.

Trimethyl-palladium(IV) and -platinum(IV) complexes containing phosphine donor ligands, including studies of 1,5,9-triethyl-1,5,9-triphosphacyclodecane and X-ray structural studies of palladium(II) and palladium(IV) complexes †

Dimethyl(2,2′-bipyridine)palladium(II) reacted with methyl triflate (CF3SO3Me) at −60 °C to form a palladium(IV) complex which reacted with a range of monodentate phosphines [PPh3, PMePh2, PMe2Ph, PCy3, P(OMe)3], 1,2-bis(diethylphosphino)ethane (depe), or syn,syn-1,5,9-triethyl-1,5,9-triphosphacyclodecane (syn,syn-Et3[12]aneP3) to form complexes containing octahedral palladium(IV) centres fac-[PdMe3(2,2′-bipy)(L)]+1–5, 11–13. The ligand depe bridges between palladium(IV) centres in a binuclear complex (11), the triphosphine forms both mononuclear (13) and binuclear species (12), and representative complexes of other bidentate nitrogen donor ligands have also been prepared, [PdMe3(N–N)(PMe2Ph)][O3SCF3] [N–N = 1,10-phenanthroline (phen) 6 or N,N,N′,N′-tetramethylethylenediamine (tmen) 7]. The first structural analysis of an organopalladium(IV) phosphine complex is reported, and octahedral 6 and platinum(IV) complexes [PtMe3(2,2′-bipy)(L)][O3SCF3] [L = PPh38, PMePh29 or PMe2Ph 10] have been isolated. All of the palladium(IV) complexes reductively eliminate ethane on decomposition to form palladium(II) species, where the monodentate phosphines form [PdMe(N–N)(L)]+1a–7a; a structural analysis of square-planar [PdMe(2,2′-bipy)(PMe2Ph)][O3SCF3] 3a is reported. The stability of palladium(IV) complexes decreases in the order PMe2Ph > PMePh2 > PPh3, and for complexes of PMe2Ph there is a stability order phen > 2,2′-bipy > tmen for [PdMe3(bidentate ligand)(PMe2Ph)]+.

Pd(II) Complexes with Bidentate Nitrogen-Donor Chelating Ligands: Very Versatile and Active Catalyst Precursors for the CO/Olefin Co- and Terpolymerization Reactions

The perfect alternating CO/olefin copolymers constitute an important class of new materials. Their synthesis requires a catalyst; in general, the applied catalytic systems are formed by a palladium(II) salt, modified by diphosphine or dinitrogen chelating ligands, in the presence of a BrØnsted acid as cocatalyst and, frequently, an oxidant such as 1,4-benzoquinone. Alcoholic medium is generally preferred. This overview will report on the main catalytic systems based on bidentate nitrogen-donor chelating ligands; particular attention will be dedicated to the CO/styrene copolymerization. A detailed analysis of several parameters influencing the yield and the quality of CO/styrene polyketone will be presented, together with the discussion of the control of the stereochemistry of the insertion of styrene in the growing chain.

2,2′-Bipyridyl and 1,10-phenanthroline adducts of the diborane (4) compound B 2 (1,2-S 2C 6H 4) 2

The syntheses and structures of the 2,2′-bipyridyl and 1,10-phenanthroline adducts of the diborane (4) compound B 2 (1,2-S 2C 6H 4) 2 are described. In both cases, the bidentate nitrogen donor ligands bridge the B–B bond, one nitrogen being bonded to each boron.

New chiral bidentate nitrogen donor ligands: synthesis of 1,2-diiminophosphoranes and their palladium complexes

Abstract The reaction of 1,2-diamines 1a-c with Ph3PBr2 in the presence of triethylamine gives rise to the corresponding diphosphonium salts 2a-c in good yields. Treatment of these salts with NaH at room temperature in CH2Cl2 affords the diiminophosphoranes 3a-c in near quantitative yields. Derivatives 3a,b react with (CH3CN)2PdCl7 giving stable (diiminophosphorane)PdCl2 complexes 4a,b. The solid state structure of complex 4a is described.

Selectivity in reductive elimination and organohalide transfer from methyl(aryl) benzylpalladium(IV) complexes of bidentate nitrogen donor ligands, PdBrMe(Ar)(CH 2Ph)(L 2)

Oxidative addition of iodoarenes to bis(dibenzylideneacetone)palladium(0) in the presence of N,N,N′,N′-tetramethylethylenediamine (tmeda) affords PdlAr(tmeda) (Ar  4-MeC 6H 4, 4-MeOC 6H 4, 4-Me(O)CC 6H 4, 4-O 2NC 6H 4, 3-MeOC 6H 4) in high yield. Some of these complexes (Ar  4-MeC 6H 4, 4-MeOC 6H 4, 3-MeOC 6H 4) react with LiMe to form PdMeAr(tmeda), and the methyl(aryl)palladium(II) complexes react with 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) to afford PdMeAr(L 2); PdMePh(phen) may be obtained similarly. All of the diorganopalladium(II) complexes of bpy and phen react with benzyl bromide to form PdBrMeAr(CH 2Ph)(L 2) but a complex could not be isolated for Ar  3-MeOC 6H 4, L 2 = bpy. The isolated palladium(IV) complexes react with PdMe 2(bpy) at −20°C in (CD 3) 2CO to selectively transfer benzyl bromide to give PdMeAr(L 2) and PdBrMe 2(CH 2Ph)(bpy) respectively. The complexes PdBrMeAr(CH 2Ph)(bpy) (Ar  Ph, 4-MeC 6H 4, 4-MeOC 6H 4) undergo selective reductive elimination of ArMe in CDCl 3 to form PdBr(CH 2Ph)(L 2), but PdBrMeAr(CH 2Ph)(phen) (Ar  Ph, 4-MeC 6H 4, 4-MeOC 6H 4, 3-MeOC 6H 4) give mixtures of PdBr(CH 2Ph)(phen) and MeAr together with lesser amounts of PdBrMe(phen) and ArCH 2Ph (ca. 10–20%).

η3-Allyl molybdenum dithiophosphate and dithiophosphinate complexes with uni- and bidentate nitrogen donor ligands. X-ray structure of [Mo 2( η3-C 3H 5) 2(CO) 4{S 2P(OEt) 2} 2( μ-NH 2NH 2)

The bis(nitrile) complex [Mo( η 3-C 3H 5)(CO) 2(NCMe) 2Br] ( 1) reacts with ammonium diethyldithiophosphate or sodium diphenyldithiophosphinate to afford [Mo( η 3-C 3H 5)(CO) 2(S 2PX 2)(NCMe)] ( 2, X = OEt or Ph). The labile nitrile ligand in these complexes can be replaced by unidentate N-donors, L, affording mononuclear [Mo( η 3-C 3H 5)(CO) 2(S 2PX 2)(L)] ( 3, L = 4-NH 2C 6H 4Me or py). Reactions of 2 with 0.5 equiv. of bidentate donors such as hydrazine or pyrazine produces binuclear complexes [Mo 2( η 3-C 3H 5) 2(CO) 4(S 2PX 2) 2( μ-NN)] ( 4, NN = N 2H 4 or pyrazine). An X-ray structure determination carried out on [Mo 2( η 3-C 3H 5) 2(CO) 4{S 2P(OEt) 2} 2( μ-NH 2NH 2)] ( 4a), showed the hydrazine bridge holding together two pseudo-octahedral ‘Mo( η 3-C 3H 5)(CO) 2{S 2P(OEt) 2} 2’ fragments.