Search

The synthesis of palladium cyclometallated compounds with thiosemicarbazone ligands is described,as well as their reactivity with bidentate phosphine ligands. The synthesis of the ligands is carried out by a condensation reaction between a ketone and a thiosemicarbazide. Subsequently, metallation proceeds, and the resulting product is reacted with the bis(diphenylphosphino)methane (dppm) using the appropriate conditions to obtain the compound with phosphine in a monodentate coordination mode.

A theoretical and experimental study of tetradentate [C,N : C,N] iminophosphorane palladacycles was carried out for the purpose of elucidating their behavior as compared to the parent Schiff base analogues to determine the prospect of encountering new A‐frame structures for the iminophosphorane derivatives. The DFT calculations were in agreement with the experimental results regarding the performance of these ligands. New insights into the chemistry of the related dinuclear species have been obtained., The experimental evidence, together with the DFT theoretical calculations prove that the tetradentate [C,N : C,N] iminophosphorane ligands behaves differently compared with the analogous diimine substrates. The results obtained from NMR spectroscopy suggest the existence in solution of E and Z conformers for the dinuclear complexes bearing chelated diphosphane donors.

In the world of science, in particular the section concerning the field of chemistry, when the results encountered during the experiment do not meet our expectations, our shrewdness may play an important role to open up new unexplored fields that could be much more interesting than what we were seeking. In those cases, our research undergoes an unforeseen shift, delivering novel and challenging results that may altogether alter our point of view and our future work. We have then struck serendipity. Specifically, in our investigation linked to palladacycles we have found that the new trends in their reactivity, as well as in their structure, have been, in many cases, related to this experience, broadening our research scope within this field. Herein, we describe our most relevant findings, which have shed new light upon the reactivity of palladacycles, thus opening new routes that lead to novel unexpected structures.

Transition metal complexes are useful in organic synthesis due to the capability of the metal to activate substrates [1-2]; in particular, cyclometallation reactions may lead to novel routes in organic synthesis. Thiosemicarbazones show a high coordinative capacity given that they possess several potential donor atoms through which they can bind to transition metals. In addition, thiosemicarbazones as well as their semicarbazones analogues have considerable biological and pharmacological interest [3] because of their antibacterial, antiviral and antitumor activity. Their derivatives with ferrocenyl phosphines such as 1,1′‑bis(diphenylphosphino)ferroceno (dppf) show a wide range of applications [4]. This communication includes the preparation and characterization of a series of thiosemicarcarbazones and of their organometallic complexes with palladium and iron. Acknowledgments We wish to thank the financial support received from the Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia Competitiva Programme Projects GRC2015/009. References: [1]- R. N. Prabhu; R. Ramesh, Tetrahedron Lett., 2013, 54, 1120. [2]- R. N. Prabhu; R. Ramesh, Tetrahedron Lett., 2012, 53, 5961. [3] S. Cruz; S. Bernes; P. Sharma; R. Vazquez; G. Hernandez; R. Potillo; R. Gutierrez, Appl. Organomet. Chem., 2010, 24, 8. [4]- A. Togni; T. Hayashi, Ferrocenes, 1995.

Treatment of a or b with Li2[PdCl4] in methanol at room temperature for 48 h, gave the tetrametallic chlorine bridged complexes [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]}(μ-Cl)]2, 1a and 1b, containing a cyclic acetal on the metallated cyclopentadienyl ring. The reactions of 1a and 1b with the Ph2P(CH2)nPPh2 diphosphines in a 1:1 ratio gave the tetrametallic species [{Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]}(Cl)}2(μ-Ph2P(CH2)nPPh2)], n = 1–4 as appropriate, 2a–5a and 2b–5b, with the diphosphine in a bridging mode and terminal chlorine ligands. Treatment of 1a and 1b with monophosphines yielded the dimetallic compounds [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]}(Cl)(L)] (L = PPh3, PPh2Me, PPh2Et) 6a–8a and 6b–7b. Reaction of the phosphine derivatives with aqueous acetic acid gave the corresponding functionalized compounds with transformation of the 1,3-dioxane ring into a formyl group on the metallated ring 9a–15a and 9b–14b. Reaction of 8a with acetic acid in methanol gave [Pd{CpFe[η5-C5H2{CH(OMe)2}C(H)N-2,4,6-Me3C6H2]}(Cl)(PPh2Et)] 16a, after a transacetalization reaction with an acetal moiety –CH(OMe)2 on the metallated five-membered ring. The molecular structure of compound 16a has been determined by X-ray diffraction analysis.

Bimetallic cyclometallated palladium(II) complexes readily react with silver perchlorate and tertiary diphosphines to give dipalladium compounds with terdentate [C,N,S] thiosemicarbazones, and with bridging and chelating [P,P] ligands, of the type [Pd(Ph2PCH2PPh2-P,P){Pd[4-MeOC6H3C(Me)NNC(S)NHMe](Ph2PCH2PPh2)-P,S}] [ClO4]2, 1a. The crystal structures of complexes [PdCl2{Pd[2-MeOC6H3C(Me)NNC(S)NHMe](Ph2PC(CH2)2PPh2)-P,S}] and [Pd(Ph2PCH2PPh2-P,P){Pd[3-MeOC6H3C(Me)NNC(S)NHMe](Ph2PC(CH2)2P-Ph2)-P,S}]-[ClO4]2, 6 and 4a, respectively, are the first reported examples of palladacycles with the diphosphine Ph2PC(CH2)2PPh2, bis(diphenylphosphine)cyclopropane (dcpc), in the bridging mode. The short-bite diphosphines produce strained four-membered rings at the metal; the structures for 1a and 4a show the P–C–P carbon atom puckered away from the metal coordination plane.

Thiosemicarbazones are formed by the condensation of an aldehyde or ketone with a thiosemicarbazide. They have high coordinative capacity given that they have several potential donor atoms through which they can bind to transition metals. This coordinative capacity can be increased if the R1 and R2 substituents include additional donor atoms. In addition, thiosemicarbazones as well as their semicarbazones analogues have considerable biological and pharmacological interest because of their antibacterial, antiviral and antitumor activity [1-2]. This communication includes the preparation and characterization of a series of thiosemicarcarbazones and their applications in the synthesis of palladium organometallic compounds [3-4]. Acknowledgments We wish to thank the financial support received from the Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia Competitiva Programme Projects GRC2015/009. References [1] S. Cruz; S. Bernes; P. Sharma; R. Vazquez; G. Hernandez; R. Potillo; R. Gutierrez, Appl. Organomet. Chem., 2010, 24, 8. [2] A. Garoufis; S. K. Hadjikakou; N. Hadjiliadis, Coord. Chem. Rev., 2009, 253, 1384. [3] P. Kalaivani; R. Prabhakaran; F. Dallemer; P. Poornima; E. Vaishnavi; E. Ramachandran; V. V. Padma; R. Renganathan; K. Natarajan, Metallomics, 2012, 4, 101. [4] E. Budzisz; R. Bobka; A. Hauss; J. N. Roedel; S. Wirth; I. P. Lorenz; B. Rozalska; M. Wieckowska-Szakiel; U. Krajewska; M. Rozalski, Dalton Transactions, 2012, 41, 5925.

Treatment of the mononuclear complex [Pd{2,4-(MeO 2 )C 6 H 2 C(H) N(Cy)- C6,N }{(Ph 2 P) 2 C CH 2 - P,P ′}][PF 6 ] ( 1 ) with methyl 2-oxocyclopentanecarboxilate, α-acetylbutyrolactone or methyl phenylsulfonylacetate in the presence of anhydrous sodium carbonate yielded the addition products [Pd{2,4-(MeO) 2 C 6 H 2 C(H) N(Cy)- C6,N }{(Ph 2 P) 2 CHCH 2 C(R 1 )(R 2 )- P,P ′}][PF 6 ] (R 1 = COOCH 3 , R 2 = COCH 2 CH 2 CH 2 , 2 ; R 1 = COCH 3 , R 2 = COOCH 2 CH 2 , 3 ; R 1 = COOCH 3 , R 2 = SO 2 Ph, 4 ) in high yield. The existence of two chiral carbon atoms in the diphosphine moiety produces the existence of optical isomers. Reaction of 1 with acetone and potassium tert-butoxide afforded complex [Pd{2,4-(Me) 2 C 6 H 2 C(H) N(Cy)- C6,N }{(Ph 2 P) 2 CHCH 2 CH 2 COCH 3 - P,P ′}][PF 6 ] ( 5 ), via C–C bond formation. Complex 1 reacts in methanol and in ethanol to give the corresponding addition products [Pd{2,4-(MeO) 2 C 6 H 2 C(H) NCy- C6,N }{(Ph 2 P) 2 CHCH 2 OR- P,P ′}][PF 6 ] (R = CH 3 , 6 ; R = CH 2 CH 3 , 7 ) , via C–O bond formation. Treatment of complex 1 with cyclohexylamine or dimethylhidrazine gives place to [Pd{2,4-(MeO) 2 C 6 H 2 C(H) N(Cy)- C6,N }{(Ph 2 P) 2 CHCH 2 N(H)R– P,P ′}][PF 6 ] (R = C 6 H 11 , 8 ; R = N(CH 3 ) 2 , 9 ), via C–N formation. The crystal structure of 7 has been determined by X-ray crystallography and comprises equimolar amounts of the (C16 R ) and (C16 S ) enantiomers. Reaction of compound 1 with dl -alanine or dl -metionine and anhydrous sodium carbonate yields [Pd{2,4-(MeO) 2 C 6 H 2 C(H) N(Cy)- C6,N }{(Ph 2 P) 2 CHCH 2 NHCH(R 1 )(R 2 )- P,P ′}][PF 6 ] (R 1 = CH 3 , R 2 = COOH, 10 ; R 1 = CH 2 CH 2 SCH 3 , R 2 = COOH, 11 ). Treatment of complex 1 with piperazine give rise to the dinuclear compound [{Pd[2,4-(MeO) 2 C 6 H 2 C(H) N(Cy)- C6,N ]} 2 {(Ph 2 P) 2 CHCH 2 N(CH 2 CH 2 ) 2 NCH 2 CH(PPh 2 ) 2 - P,P,P ′ ,P ′}][PF 6 ] 2 12 , in which each N–H bond of the piperazine has been added to the vinylidene bond of one vdpp ligand.

The Cover Feature shows four structures depicting (clockwise from the top‐left corner) a beautiful tetranuclear layered compound, a bis‐pseudopentacoordinated palladium moiety, the only known trinuclear thiosemicarbazone palladacycle, and the sandwiched coordination of the potassium cation by small crown ether rings attached to the metallated phenyl enclosures of a dinuclear diphosphine‐bridged palladium complex. All of these unexpected findings put forward the presence of serendipity in the reactivity of palladacycles and highlight the relevance of such an experience in their chemistry. More information can be found in the Review by A. Fernández‐Figueiras et al. on page 754 in Issue 10, 2018 (DOI: https://doi.org/10.1002/open.201800036).

The reaction of the tetranuclear halide-bridged complexes 1−2(a−d) with Ph2PCH2PPh2 (dppm) or Ph2PC( CH2)PPh2 (vdpp) in 1:2 molar ratio and NH4PF6 afforded the novel tetarnuclear palladacycles 3−6 (a, c, d) as 1:2 electrolytes with bridging diphosphine and halogen ligands. The structure of 4a has been determined by X-ray diffraction analysis, and represents the first example of a tetranuclear palladacycle with bridging dppm and halogen ligands. Reaction of 1−2(a−d) with (Ph2PCH2CH2)2PPh (triphos) in 1:2 molar ratio gave 7(a−d) bearing two pentacoordinated palladium atoms. The structure of 7a, as determined by X-ray diffraction analysis, shows the distorted square pyramidal geometry around the metal centers. Treatment of 1−2(a−d) with dppm, vdpp or Ph2PN(Me)PPh2 (dppma) in 1:4 molar ratio gave the dinuclear palladacycles 8−10(a−d) with a chelating diphosphine ligand at each metal center; further treatment of 9(a−c) with the nucleophiles pyrrolidine, piperidine, morpholine or 4-methyl-piperidine gave the Michael addition derivatives 11−12(a−c), 13b, 13c and 14c, promoted by the withdrawing effect of the palladacycle which activates the C CH2 double bond.

Treatment of the thiosemicarbazones 4-FC6H4C(Me) NN(H)C( S)NHR, (R = Me, a; Ph, b) and 2-ClC6H4C(Me) NN(H)C( S)NHR (R = Ph, c) with lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complex [Pd{4-FC6H3C(Me) NN C(S)NHR}]4 (1a, 1b) and [Pd{2-ClC6H3C(Me) NN C(S)NHPh}]4 (1c). Reaction of these tetramers with the diphosphines dppe, t-dppe, dppp or dppb in a 1:2 molar ratio gave the dinuclear cyclometallated complexes [(Pd{4-FC6H3C(Me) NN C(S)NHR})2(μ-Ph2P(CH2)nPPh2)], (n = 2, 2a, 2b; 3, 4a, 4b; 4, 5a, 5b), [(Pd{4-FC6H3C(Me) NN C(S)NHPh})2(μ-Ph2PCH CHPPh2)], (3a, 3b) and [(Pd{2-ClC6H3C(Me) NN C(S)NHR})2(μ-Ph2P(CH2)nPPh2)], (n = 2, 2c, 2d; 3, 4c, 4d; 4, 5c, 5d), [(Pd{2-ClC6H3C(Me) NN C(S)NHPh})2(μ-PPh2CH CHPPh2)], (3c, 3d). The X-ray crystal structure of the ligand b and the complexes 3c, 4a and 4d were determined. The structures of complexes 4a and 4d show that the different disposition of the chain cyclometallated of the thiosemicarbazones (in the same orientation or in the opposite one) is due to the different H bonds produced.

Treatment of N-(2-bromobenzylidene)cyclohexylamine, 2-BrC6H4C(H)NCy (a), with tris(dibenzylideneacetone)palladium(0) in refluxing benzene gave the cyclometallated compound [Pd{C6H4C(H)NCy}(Br)]2 (1). Treatment of 1 with thallium acetylacetonate gave the mononuclear cyclometallated compound [Pd{C6H4C(H)NCy}(MeCOCHCOMe)] (2). Reaction of a with palladium(II) acetate in refluxing acetic acid gave the dinuclear Pd(II) compound [Pd{2-BrC6H3C(H)NCy}(O2CMe)]2 (3). Treatment of 3 with aqueous sodium chloride gave the dimer complex [Pd{2-BrC6H3C(H)NCy}(Cl)]2 (4). Reaction of 4 with tertiary phosphines gave the cyclometallated complexes [Pd{2-BrC6H3C(H)NCy}(L)] (5: L=PPh3; 6: L=PEtPh2; 7: L=PMePh2), with the phosphine ligand trans to the imine nitrogen atom. Treatment of 2-Br4,5-(MeO)2C6H2C(H)NCH2CH2NMe2 (b), with palladium(II) chloride in refluxing octane or with tris(dibenzylideneacetone)palladium(0) gave [Pd{4,5-(MeO)2C6H2C(H)NCH2CH2NMe2}(X)] (8: X=Cl; 16: X=Br, respectively) and with the ligand as [C, N, N] terdentate. Treatment of 8 with tertiary phosphines gave [Pd{4,5-(MeO)2C6H2C(H)NCH2CH2NMe2}(Cl)(L)] (9: L=PPh3; 10: L=PEtPh2; 11: L=PMePh2). Reaction of 1,4-{2-Br4,5-(MeO)2C6H2C(H)N}2C6H4 (c), with PdCl2, Li2[PdCl4] or K2[PdCl4] gave the tetranuclear compound [1,4-{Pd[4,5-(MeO)2C6H2C(H)N](Cl)}2C6H4]2 (12), which when treated with tertiary phosphines gave the dinuclear species 13–15. The molecular structure of 2 has been determined by X-ray crystallography.

The oxidative addition reaction of 1,4-(CN(H)CH2CH2Me2)2-2,5-Cl2C6H2 with tris(dibenzylideneacetone)dipalladium(0) in benzene gave the doubly cyclometallated compound [(Cl)Pd{Me2NCH2CH2N(H)C}C6H2{C(H)NCH2CH2NMe2}Pd(Cl)] (1) with each palladium atom C,N,N′ bonded to the ligand. Treatment of 1 with thallium acetylacetonate gave the dinuclear cyclometallated complex 2 with two chelating acetylacetonate ligands. Reaction of 1 with tertiary monophosphines in a 1–phosphine 1:2 molar ratio gave dinuclear cyclometallated complexes 3–7, in which the palladiumNMe2 bond has been broken, whereas treatment of 1 with silver perchlorate, followed by reaction with PPh3 in a 1–phosphine 1:2 molar ratio gave cyclometallated complex 4 where the ligand remains C,N,N′ bonded and the chloride ligand has been substituted by triphenylphosphine. Treatment of 1 with tertiary diphosphines leads to dinuclear compounds 8, 10 and 11, whilst previous treatment of 1 with silver perchlorate followed by the diphosphine 1,4-bis(diphenylphosphino)butane (dppb) in a 1–diphosphine 1:1 molar ratio yielded the tetranuclear complex 9. Reaction of 1 with the tertiary triphosphine bis(2-diphenylphosphinoethyl)phenylphosphine in 1:2 molar ratio gave the complex [{(Ph2PCH2CH2)2PPh-P,P,P}Pd{Me2NCH2CH2N(H)C}-C6H2{C(H)NCH2CH2NMe2}Pd{(Ph2PCH2CH2)2PPh-P,P,P}][Cl]2 (12) in which both palladium atoms are pentacoordinated. The crystal structures of 1 and 12 are described.

Treatment of the cyclometallated complexes [Pd{4-MeC 6 H 3 C(Me)NN(H)C(O)NH 2 }(Cl)] ( a ), [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }(Cl)] ( b ) and [Pd{3,4-Me 2 C 6 H 2 C(Me)NN(H)C(O)NH 2 }(Cl)] ( c ) with tertiary monophosphine ligands in a complex–phosphine 1:1 molar ratio yielded [C, N] bonded cyclometallated complexes [Pd{4-MeC 6 H 3 C(Me)NN(H)C(O)NH 2 }(Cl)(L)] ( 1a – 4a ), [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }(Cl)(L)] ( 1b – 4b ) and [Pd{3,4-Me 2 C 6 H 2 C(Me)NN(H)C(O)NH 2 }(Cl)(L)] ( 1c – 4c ), [L=PPh 3 , PMePh 2 , PEtPh 2 and PEt 2 Ph]. Reaction of a , b and c with silver perchlorate, prior to the treatment with the monophosphine gave the [C, N, O] bonded cyclometallated complexes [Pd{4-MeC 6 H 3 C(Me)NN(H)C(O)NH 2 }(L)][ClO 4 ] ( 5a – 8a ), [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }(L)][ClO 4 ] ( 5b – 8b ) and [Pd{3,4-Me 2 C 6 H 2 C(Me)NN(H)C(O)NH 2 }(L)][ClO 4 ] ( 5c – 8c ). Reaction of a , b and c with tertiary monophosphines in a complex–phosphine 1:2 ratio gave the C only bonded non-cyclometallated complexes [Pd{4-MeC 6 H 3 C(Me)NN(H)C(O)NH 2 }(PEt 2 Ph) 2 (Cl)] ( 9a ), [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }(PPh 3 ) 2 (Cl)] ( 9b ) and [Pd{3,4-Me 2 C 6 H 2 C(Me)NN(H)C(O)NH 2 }(PEt 2 Ph) 2 (Cl)] ( 9c ). Treatment of a , b and c with the triphosphine bis(2-diphenylphosphinoethyl)phenylphosphine (trifos) yielded the non-cyclometallated complexes [Pd{4-[MeC 6 H 3 C(Me)NN(H)C(O)NH 2 }{L- P , P , P }][Cl] ( 10a ), [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }{L- P , P , P }][Cl] ( 10b ) and [Pd{3,4-Me 2 C 6 H 2 C(Me)NN(H)C(O)NH 2 }{L- P , P , P }][Cl] ( 10c ) (L=(Ph 2 PCH 2 CH 2 ) 2 PPh). The complexes were characterised by their elemental analysis (C, H, N) and by IR and 31 P-{ 1 H} and 1 H-NMR spectroscopy. [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }(PPh 3 )][ClO 4 ] ( 5b ) and [Pd{C 6 H 4 C(Et)NN(H)C(O)NH 2 }{(Ph 2 PCH 2 CH 2 ) 2 PPh- P , P , P }][Cl] ( 10b ) were characterised crystallographically.

Treatment of the thiosemicarbazones 3-CH3(CH2)5OC6H4C(Me)NN(H)C(S)NH2 (a), 4-MeC6H4C(Me)NN(H)C(S)NH2 (b), C6H5C(Et)NN(H)C(S)NH2 (c), C6H5C{CH3(CH2)10}NN(H)C(S)NH2 (d) and 4-MeC6H4C(Me)NN(H)C(S)NHMe (e) with K2[PtCl4] gives tetranuclear platinum(II) compounds 1a–1e with deprotonation of the NH group and with the ligand acting as a terdentate [C,N,S] moiety. Reaction of 1a–1e with PPh3 and of 1a with P(4-MeOC6H4)3 yielded mononuclear species 2a–2e and 3a, respectively. Treatment of 1a with the diphosphines Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe), Ph2P(CH2)3PPh2 (dppp), Ph2P(CH2)4PPh2 (dppb), Ph2P(CH2)5PPh2 (dpppe), Ph2P(CH2)6PPh2 (dpph), and 1,1′-ferrocenebis(diphenylphosphine) (dppf) gives dinuclear compounds 4a–10a. In all cases the PdSchelating bond is strong enough to withstand reaction with the phosphorus ligands without bond cleavage. The molecular structure of 2b has been determined by X-ray crystallography. Mononuclear units are held together by hydrogen bonding, forming dimers in the solid state.

Treatment of the potentially terdentate ligands C6RxH5−xC(H)N–CH2CH2NMe2 [R: a (x=2), 2,4-(MeO)2; b (x=2), 3,4-(MeO)2; c (x=2), 3-Me-4-MeO; d (x=3), 2,3,4-(MeO)3; e (x=2), 4,5-(OCH2O); f (x=1), 2-NO2] with [PtMe2(COD)] gave the platinated compounds [Pt{C6RxH4−xC(H)NCH2CH2–NMe2}(Me)] with two fused five-membered rings at platinum. The crystal and molecular structure of [Pt{3-Me-4-MeOC6H2C(H)NCH2CH2NMe2}(Me)] has been determined by X-ray crystallography. The reactivity of these complexes was tested by the reactions of [Pt{2,4-(MeO)2C6H2C(H)NCH2CH2NMe2}–(Me)] with tertiary phosphines and diphosphines. In the latter case, dinuclear and mononuclear platinum complexes were synthesized, with bridging or chelating diphosphine ligands, respectively, depending on the complex/diphosphine molar ratio used. The reaction of the related potentially hexadentate ligand 1,4-[Me2NCH2CH2N(H)C]2C6H4 with [PtMe2(COD)] gave the metallated compound [(Me)Pt{Me2NCH2CH2N(H)C}C6H2{C(H)N–CH2CH2NMe2}Pt(Me)] with five fused rings.

Treatment of the semicarbazones 4-MeC6H4C(Me)NN(H)C(O)NH2 a, 3,4-Me2C6H3C(Me)NN(H)C(O)NH2 b and C6H5C(Et)NN(H)C(O)NH2 c, gave the [C,N,O] cyclometallated compounds [Pd{4-MeC6H3C(Me)NN(H)C(O)NH2}(Cl)] 1a, [Pd{3,4-Me2C6H2C(Me)NN(H)C(O)NH2}(Cl)] 1b and [Pd{C6H4C(Et)NN(H)C(O)NH2}(Cl)] 1c, after CH activation. Treatment of compounds 1a, 1b, and 1c with silver perchlorate followed by treatment with tertiary diphosphine ligands gave the dinuclear [C,N,O] cyclometallated compounds [{Pd[4-MeC6H3C(Me)NN(H)C(O)NH2]}2(μ-L)][ClO4]2 2a–7a, [{Pd[3,4-Me2C6H2C(Me)NN(H)C(O)NH2]}2(μ-L)][ClO4]2 2b–7b, [{Pd[C6H4C(Et)NN(H)C(O)NH2]}2(μ-L)][ClO4]2 2c–7c, [L=Ph2P(CH2)4PPh2 (dppb), Ph2P(CH2)3PPh2 (dppp), Ph2P(CH2)2PPh2 (dppe), trans-Ph2PCHCHPPh2 (trans-dppe), Ph2PC(CH2)PPh2 (vdpp) and Ph2PCH2PPh2 (dppm)] as 1:2 electrolytes. Reaction of 1a and 1c with diphosphines gave the dinuclear [C,N] cyclometallated compounds [{Pd[4-MeC6H3C(Me)NN(H)C(O)NH2](Cl)}2(μ-L)] 8a, 9a, [{Pd[C6H4C(Et)NN(H)C(O)NH2](Cl)}2(μ-L)] 8c, 9c, [L=Ph2P(CH2)3PPh2 (dppp) and Ph2P(CH2)4PPh2 (dppb)]. The complexes were characterised by their elemental analysis (C,H,N) and by IR and 31P{1H} and 1H-NMR data, and [{Pd[C6H4C(Et)NN(H)C(O)NH2]}2(μ-Ph2P(CH2)3PPh2)][ClO4]2 (3c) was characterised crystallographically.

Treatment of the cyclometallated complexes [{Pd[3-(CHO)C 6 H 3 C(H)NCy}(X)} 2 ] [X=Cl ( 1 ), Br ( 2 ), I ( 3 )] with tertiary monophosphines in a complex/phosphine 1:2 or 1:4 molar ratio afforded the halide-bridged cleaved [Pd{3-(CHO)C 6 H 3 C(H)NCy}(X)(L)] ( 6 – 17 ) and non-cyclometallated complexes [Pd{3-(CHO)C 6 H 3 C(H)NCy}(X)(L) 2 ] ( 18 – 23 ) (X=Cl, Br or I; L=PPh 3 , PEtPh 2 , PEt 2 Ph or PMePh 2 ), respectively. Reaction of 6 – 17 with cyclohexylamine in a complex/amine 1:1 or 1:2 molar ratio gave [Pd{3-(CyC(H)N)C 6 H 3 C(H)NCy}(X)(L)] ( 24 – 28 ) and the non-cyclometallated [Pd{3-(CyC(H)N)C 6 H 3 C(H)NCy}(X)(L)(NH 2 Cy)] ( 29 – 32 ) complexes, respectively. Compounds 18 , 19 and 22 gave [Pd{3-(CyC(H)N)C 6 H 3 C(H)NCy}(X)(PR 3 ) 2 ] ( 33 – 35 ) with two uncoordinated CN groups, when treated with cyclohexylamine. Other reaction routes are also discussed. The complexes were characterised by their elemental analysis (C, H, N) and by IR and 31 P{ 1 H} and 1 H-NMR data, and [Pd{3-(CHO)(C 6 H 3 C(H)NCy}(Br)(PEtPh 2 )] ( 12 ) was characterised crystallographically.

Treatment of Pd(AcO)2 with 1-methyl-2-phenylimidazole, and subsequent treatment with sodium chloride or sodium bromide gave the corresponding halide-bridged cyclometallated complexes [Pdo-C6H4C=NC(H)=C(H)NMe(μ-X)]2 (2, X = Cl; 3, X = Br). Complexes 2 and 3 react with tertiary diphosphines in a 1:1 molar ratio to give dinuclear cyclometallated compounds with bridging diphosphine and halogen ligands [Pdo-C6H4C=NC(H)=C(H)NMe(μ-L-L)(μ-X)]X (4–9) or with only bridging diphosphine ligands [Pdo-C6H4C=NC(H)=C(H)NMe(μ-L-L)(X)2] (10–17), [X = Cl, Br; L-L = Ph2PCH2PPh2 (dppm), Ph2PC(=CH2)PPh2 (vdpp), Ph2PCH(CH3)PPh2 (1,1-dppe), trans-Ph2P(CH=CH)PPh2 (trans-dppe), Ph2P(CH2)2PPh2 (dppe), Ph2P(CH2)3PPh2 (dppp), Ph2P(CH2)4PPh2 (dppb), as appropriate]. When the reaction is carried out in a 1:2 molar ratio and in the presence of NH4PF6 or NaClO4, mononuclear cyclometallated compounds with a chelating diphosphine ligand are obtained [Pdo-C6H4C=NC(H)=C(H)NMe(L-L-P,P)][Y] (18–27) [Y = PF6, ClO4; L-L = Ph2PCH2PPh2 (dppm), Ph2PC(=CH2)PPh2 (vdpp), Ph2PCH(CH3)PPh2 (1,1-dppe), Ph2PN(CH3)PPh2 (dppma), cis-Ph2P(CH=CH)PPh2 (cis-dppe), Ph2P(CH2)2PPh2 (dppe), Ph2P(CH2)PPh2 (dppp), Ph2P(CH2)4PPh2 (dppb)]. Compounds 18–22 and 25–27 could also be obtained by reaction of complexes 4–17 with the appropriate diphosphine and NH4PF6 or NaClO4. The diphosphines dppma and cis-dppe failed to behave as bridging ligands and only gave mononuclear compounds. The complexes were characterized by their elemental analysis (C, H, N) and by IR and 31P-1H and 1H NMR data. The X-ray crystal structure of complex 22 is described.

Treatment of N-(2-chlorobenzylidene)-N,N′-dimethylethylenediamine, 2-ClC6H4C(H)NCH2CH2NMe2, with tris(dibenzylideneacetone)dipalladium(0) in chloroform gave the oxidative addition cyclometallated product [Pd{C 6 H 4 C(H)NCH 2 CH 2 N Me2}(Cl)] (1) with the palladium atom bonded to a C,N,N′ terdentate donor ligand. Treatment of 1 with tertiary monophosphines gave the cyclometallated complexes [Pd{C 6 H 4 C(H)N CH2CH2NMe2}(Cl)(L)](2: L  PPh3; 3: L  PEtPh2; 4: L  PEt2Ph; 5: L  PEt3), where the phosphine ligand is either trans to the phenyl carbon atom (2, 3) or trans to the imine nitrogen atom (4, 5). Treatment of 1 with silver perchlorate followed by reaction with tertiary monophosphines gave the cyclometallated complexes [Pd{C 6 H 4 C(H)NCH 2 CH 2 N Me2}(L)][ClO4] (6: L  PPh3; 7: L  PEtPh2; 8: L  PEt2Ph; 9: L  PEt3). Reaction of 1 with thallium acetylacetonate gave the cyclometallated complex [Pd{C 6 H 4 C(H)N CH2CH2NMe2}(H3CCOCHCOCH3)] (10). Treatment of 1 with ditertiary diphosphines in a complex 1/diphosphine 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[C 6 H 4 C(H)N CH2CH2NMe2](Cl)}2(LL)(11: LL = trans-Ph2PCHCHPPh2; 12: LL  Ph2P(CH2)3PPh2;13: LL  Ph2P(CH2)4PPh2), where the phosphorus atom is trans to the phenyl carbon atom. Treatment of 1 with silver perchlorate followed by ditertiary diphosphines in a complex 1/diphosphine 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[C 6 H 4 C(H)NCH 2 CH 2 N Me2]}2 (LL)][ClO4]2 [14: LL=trans-Ph2PCHCHPPh2; 15: LL  Ph2P(CH2)3PPh2; 16: LL  Ph2P(CH2)4PPh2)]. Reaction of 1 with ditertiary diphosphines in a complex 1/diphosphine 1:1 molar ratio, and silver perchlorate as appropriate, gave the cyclometallated complexes [Pd{C 6 H 4 C(H)N CH2CH2NMe2}(Ph2P(CH2)2PPh2-P,P)][ClO4] (17), [Pd{C 6 H 4 C(H)N CH2CH2NMe2}(Ph2P(CH2)3PPh2-P,P)][ClO4] (18), [ Pd{C 6 H 4 C(H)N CH2CH2NMe2}(cis-Ph2PCHCHPPh2-P,P)][Cl] (19) and [Pd{C6H4C-(H)NCH2CH2NMe2}(Cl)(Ph2P(CH2)4PPh2-P,P)] (20).

Treatment of the cyclometallated halide-bridged complexes [1,4-{ Pd [2,3,4-( MeO ) 3 C 6 HC (H) = N ]( X )} 2 C 6 H 4 ] 2 (1a, 2a), [1,4-{ Pd [2,4-( MeO ) 2 C 6 H 2 C(H) = N ]( X )} 2 C 6 H 4 ] 2 (1b, 2b), [1,4-{ Pd [3-( Me -4- MeOC 6 H 2 C(H) = N ]( X )} 2 C 6 H 4 ] 2 (1c, 2c), [1,4-{ Pd [4,5-( OCH 2 O )C 6 H 2 C(H) = N ]( X )} 2 C 6 H 4 ] 2 (1d, 2d), (X = Cl, Br) with ditertiary diphosphines in a complex/diphosphine 1:4 molar ratio and ammonium hexafluorophosphate gave the dinuclear cyclometallated complexes [1,4-{ Pd[2,3,4-(MeO) 3 C 6 HC(H)N ]} 2 C 6 H 4 (LL) 2 ][PF 6 ] 2 [LL  Ph 2 PCH(CH) 3 )PPh 2 , Ph 2 P(CH 2 ) 2 PPh 2 , 3a, 4a], [1,4-{ Pd [2,4-( MeO ) 2 C 6 H 2 C(H) = N ]} 2 C 6 H 4 ( LL ) 2 ][ PF 6 ] 2 [LL  Ph 2 PCH(CH 3 ) PPh 2 , Ph 2 P(CH 2 ) 2 PPh 2 , 3b, 4b] [1,4-{ Pd [3-( Me -4- MeOC 6 H 2 C(H) = N ]} C 6 H 4 ( LL ) 2 ][ PF 6 ] 2 [LL  Ph 2 PCH(CH 3 ) PPh 2 , Ph 2 P(CH 2 ) n PPh 2 , n = 2, 3 , 3c, 4c, 5c], [1,4-{ Pd [4,5-( OCH 2 O ) C 6 H 2 C(H) = N ]} 2 C 6 H 4 ( LL ) 2 ] [ PF 6 ] 2 [ LL = Ph 2 PCH(CH 3 ) PPh 2 , Ph 2 P(CH 2 ) n PPh 2 , n = 2, 3, 4 , 3d, 4d, 5d, 6d]. The influence of ring size on the phosphorus chemical shift is discussed. The compounds were characterized by microanalysis (C, H, N), IR and 31P-{1H} and 1H NMR spectroscopy. The structure of the dinuclear cyclometallated palladium(II) complex [1,4-{ Pd [2,4-( MeO ) 2 C 6 H 2 C(H) = N ]} 2 C 6 H 4 { Ph 2 P(CH 2 ) 3 PPh 2 −PP} 2 ][ PF 6 ] 2 is described. There are two different crystallographic molecules per asymmetric unit.

Treatment of N,N-isophthalylidenebis(cyclohexylamine), 1,3-(CyNCH)2C6H4 (L2) (Cy = cyclohexyl) with palladium(II) acetate in glacial acetic acid gave after column chromatography the monocyclometallated dimer complex [{ Pd[3-(CHO)C 6 H 3 C(H)N Cy](O 2 CMe)} 2 ] (1) with a free formyl group on each phenyl ring, and a mixture of 1 with the doubly cyclometallated complex [ Pd{3-(CyNCH)C 6 H 3 C(H)N Cy}(O 2 CMe) ] (2). Treatment of 1 with cyclohecylamine gave the corresponding dimer complex [{ Pd[3-(CyNCH)C 6 H 3 C(H)N Cy]O 2 CMe)} 2 ] (17 with an uncoordinated CN group on each phenyl ring. Treatment of 1 and 2 with aqueous NaX gave the dimer complexes [{ Pd[3-(CHO)C 6 H 3 C(H)N Cy](X)} 2 ] (3: X = Cl; 4 X = Br; 5: X = I) and a mixture of 3, 4 or 5 with the doubly cyclometallated complex [{ Pd[3-(CyNCH)C 6 H 3 C(H)N Cy}(X) ] (6: X = Cl; 7: X = Br; 8: X = I), respectively. The dicyclometallated iodo complex 8 was isolated pure. Treatment of 3, 4 or 5 with cyclohexylamine in a 1 : 2 or 1 : 4 molar ratio gave the cyclometallated complexes [ { Pd[3-(CHO)C 6 H 3 C(H)N Cy}(X)(NH 2 Cy) ] (9: X = Cl; 10: X = Br; 11: X = I) and [{ Pd[3-(CyNCH)C 6 H 3 C(H)N Cy}(X)(NH 2 Cy) ] (12: X = Cl; 13: X = Br; 14: X = I), respectively; the last three compounds each contain an uncoordinated C  N group. The corresponding bromo and iodo analogues were made similarly. Treatment of 3, 4 or 5 with thallium cyclopentadienyl or thallium acetylacetonate gave the mononuclear complexes [{ Pd[3-(CHO)C 6 H 3 C(H)N Cy}(C 5 H 5 ) ] (15) and [{ Pd[3-(CHO)C 6 H 3 C(H)N Cy}(H 3 CCOCHCOCH 3 ) ] (16), respectively. Treatment of L2 with MnMe(CO)5 in a 1 : 1 molar ratio gave the monocyclometallated complex [ (OC) 4 Mn{3-(CHO)C 6 H 3 C(H)N Cy} ] (18) by cleavage of one CN bond, whereas treatment of L2 with MnMe(CO)5 in a 1 : 1.2 molar ratio produced a mixture of the doubly cyclometallated complex 19 and the monocyclometallated complex 20 without cleavage of the C  N bond. Treatment of N,N-terephthalylidenebis(cyclohexylamine), 1,4-(CyNCH)2C6H4 (L1) (Cy = cyclohexyl), with MnMe(CO)5 in a 1 : 1.2 molar ratio gave a mixture of the monocyclometallated compound [ (OC) 4 Mn{4-(CHO)C 6 H 3 C(H)N Cy} ] (22) and the monocyclometallated compound [ (OC) 4 Mn{4-(CyNCH)C 6 H 3 C(H)N Cy} ] (23); compound 22 was isolated in a pure state.

The reaction of the halide-bridged dimer complex [{ Pd{2,3,4-(MeO) 3 C 6 HC(H)N Cy}Cl}2] with Ph2PC(CH2)PPh2 (vdpp) in a dimer/diphosphine 1 : 1 molar ratio gives a yellow solid, from whose dichloromethane solution suitable crystals of [{ Pd[2,3,4- (MeO) 3 C 6 HC(H)N Cy]}2{μ-Ph2PC(CH2)PPh2}Cl2] (1) were grown. The structure of 1 has been determined by X-ray crystallography. In the structure there are two [{ Pd[2,3,4-(MeO) 3 C 6 HC(H)N Cy]}Cl] units linked by a ditertiary diphosphine (vdpp) with each palladium atom showing a square-planar environment. Compound 1 is a non-electrolyte, as compared to a 1 : 1 electrolyte structure found for a similar complex.

Treatment of 1,4-{2,3,4-(MeO)3C6H2C(H)=N-}2C6H, (a) or 1,4-{4,5-(OCH2O)C6H 3C(H)=N-}2-C6H4 (b) with palladium(II) acetate gave the cyclometallated acetato-bridged complexes [1,4-{ Pd [2,3,4-(MeO) 3 C 6 HC(H)=N ](O2CMe)}2C6H4]n (1a) and [1,4- Pd[4,5-(OCH 2 O)C 6 H 2 C(H)=N ](O2CMe)}2-C6H4]n (1b). These were converted into the analogous halide-bridged complexes by treatment with NaX (2a, 2b X = Cl; 3a, 3b X = Br). Reaction of a or b with PdCl2 also affords the chloro-bridged complexes 2a and 2b, which reacted with LiBr to give the bromo-bridged complexes 3a and 3b. The structure of 3a is described. This is the first example of a structurally characterized tetranuclear cyclometallated bromo-bridged palladium(II) complex. Crystals are triclinic, space group P 1 , with a 1109.1(4), b 1181.5(4), c 1481.5(5) pm, α 77.33(3), β 80.04(3), γ 82.50(3), U 1.857(1) nm3, Z = 1, R = 0.0558 and RW = 0.0610, for 3871 independent reflections with I > 2.0σ-(I). The structure is a centrosymmetric tetranuclear palladium(II) dimer with symmetrically bridging bromine atoms and non-bonding Pd ⋯ Pd distance of 366.2(5) pm.

In the title compound, cis-[PdBr 2 {Ph 2 P(CH 2 ) 3 PPh 2 }], the Pd atom is coordinated to the diphosphine ligand through the P atoms and to two bromo ligands in a slightly distorted square-planar arrangement. The displacements of the P atoms from the PdBr 2 plane are 0.066 and -0.349 A, a consequence of the steric strain caused by the eclipsing of bonds in the alkyl chain of the phosphine.