Search

Treatment of bis(iminophosphorane)phosphane ligands 2a–2e with Li2PdCl4 gave a set of novel diphosphane-derived complexes bearing two metallacycle rings, each one enclosing a P=N double bond: the unprecedented bis(iminophosphorane)phosphane-[C,N,S] palladacycles. In the case of the ligand derived from bis(diphenylphosphino)methane, 2a, both the single and the double palladacycle complexes were obtained. Reaction of 3a with bis(diphenylphosphino)ethane did not yield the expected product with the diphosphane bonded to both palladium atoms, but rather the novel coordination compound 5. The crystal structures of 3c and 5 are described.

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.

Treatment of the double nuclear complex 1a, di-μ-cloro-bis[N-(4-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph2PCH2CH2)2PPh (triphos) and NH4PF6 gave the single nuclear species 2a, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate). Reaction of 2a with Ph2PCH2CH2NH2 in refluxing chloroform via a condensation reaction of the amine and formyl groups to produce the C=N double bond, gave 3a, 1-N-(cyclohexylamine)-4- N-(diphenylphosphinoethylamine)palladium(triphos)(hexafluorophasphate); a potentially bidentate [N,P] metaloligand. However, attempts to coordinate a second metal by treatment of 3a with [PdCl2(PhCN)2] were to no avail. Notwithstanding, complexes 2a and 3a left to stand in solution spontaneously self-transformed to give in either case the double nuclear complex 10, 1,4-N,N-terephthalylidene(cyclohexilamine)-3,6-[bispalladium(triphos)]di(hexafluorophosphate), after undergoing further metalation of the phenyl ring, then bearing two mutually trans [Pd(Ph2PCH2CH2)2PPh)-P,P,P] moieties: an unprecedented and serendipitous result indeed. On the other hand, reaction of the double nuclear complex 1b, di-μ-cloro-bis[N-(3-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph2PCH2CH2)2PPh (triphos) and NH4PF6 gave the single nuclear species 2b, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate), Treatment of 2b with H2O/glacial MeCOOH gave cleavage of the C=N double bond and of the Pd···N interaction, yielding 5b, isophthalaldehyde-6-palladium(triphos)hexafluorophosphate, which then reacted with Ph2P(CH2)3NH2 to yield complex 6b, N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)di(hexafluorophosphate), with two pairs of non-coordinated nitrogen and phosphorus donor atoms. Treatment of 6b with [PdCl2(PhCN)2], [PtCl2(PhCN)2], or [PtMe2(COD)] gave the new double nuclear complexes 7b, 8b and 9b, palladiumdichloro-, platinumdichloro- and platinumdimethyl[N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)(hexafluorophosphate)-P,P], respectively, showing the behavior of 6b as a palladated bidentate [P,P] metaloligand. The complexes were fully characterized by microanalysis, IR, 1H, and 31P NMR spectroscopies, as appropriate. The X-ray single-crystal analyses for compounds 10 and 5b have been previously described as the perchlorate salts by JM Vila et al.

Cyclometallated compounds have been extensively studied, in particular those with palladium and platinum. This is because of their possible applications in medicinal chemistry, as anticancer or antimicrobial agents; in some cases, with similar results as cisplatin, carboplatin or oxaliplatin. What is also remarkable is their use as homogeneous catalysts, for example, in cross coupling reactions such as Suzuki–Miyaura or Mizoroki–Heck. Herein, we report the synthesis of different thiosemicarbazone ligands, which will be reacted with a palladium or platinum salt, to give the corresponding cyclometallated compounds; in addition, their reactivity with bis(diphenylphosphino)methane (dppm) will be studied. Characterization has been carried out by elemental analysis, IR spectroscopy, 1H and 31P NMR spectroscopy. Additionally, 1c has been studied by X-ray diffraction Francisco Reigosa wants to thank the Spanish Government (AEI) for their financial support through an FPU grant (number 13/05014). The authors thank funding from Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia program (GRC 2019/014) SI

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.

Treatment of the imines a–c with palladium(II) acetate in acetic acid yielded the μ-acetate dinuclear complexes 1a–c, which readily reacted with sodium chloride or bromide to provide μ-halide analogues. The reaction of the latter with nitrogen, phosphorus and oxygen donor nucleophiles yielded new imine palladacycles following the cleavage of the Pd2X2 unit. The complexes were fully characterized by microanalysis, 1H, 13C and 31P NMR spectroscopies, as appropriate. The compounds were applied as catalysts in the Suzuki–Miyaura coupling reaction in aqueous and semi-aqueous media.

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.

A solution of compound 3 in dichloromethane produced a crystalline solid whose crystal structural analysis yielded a molecular structure with an asymmetric unit comprising two different palladacycles: the acetylacetonate complex 3 and the chloro–bridged dinuclear compound 2. The parent solution was examined by IR and NMR spectroscopy showing the conversion of 3 into 2, which may be due to traces of chloride ion in the form of acid present in the solvent, whereas an acid‑free solution of compound 3 remained unchanged. DFT calculations of the transformation have been carried out.

Reaction of the thiosemicarbazones 3-FC6H4C(Me)=NN(H)C(=S)NHR, (R = Et, a; Ph, b) with potassium tetrachloropalladate(II) in ethanol, lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complexes [Pd{3-FC6H3C(Me)=NN=C(S)NHR}]4 (1a, 1b). Reaction of 1a, 1b with the tertiary phosphines dppm, dppe, dppp, dppb or trans-dppen in 1:2 M ratio gave [(Pd{3-FC6H3C(Me)=NN=C(S)NHR})2(μ-PPh2(CH2)nPPh2)], (n = 1, 2a-b; 2, 3a-b; 3, 4a-b; 4, 5a-b), [(Pd{3-FC6H3C(Me)=NN=C(S)NHR})2(μ-PPh2CH=CHPPh2)], (6a-b). Treatment of 1a, b with dppm in 1:4 M ratio gave the mononuclear complexes [Pd{3-FC6H3C(Me)=NN=C(S)NHR}(Ph2PCH2PPh2-P)] (7a-b). Reaction of the latter with an equimolar amount of [PdCl2(PhCN)2] gave [PdCl2{Pd[3-FC6H3C-(Me)=NN=C(S)NHR](PPh2CH2PPh2)-P,S}], (8a-b). The molecular structure of ligands a and b, and of complex 6a have been determined by X-ray diffraction analysis. The ligands and complexes have also been characterized by Density Functional Theory (DFT) calculations in order to obtain structural information for the species for which no X-ray data were available.

Herein we report a Suzuki-Miyaura type cross-coupling between an aryl halide and a functionalized boronic acid palladacycle in the absence of an external catalyst. This reaction is an unprecedented case of catalysis in palladium metallacycle chemistry.

Palladacycles of the type [Pd2(Ph2PCH2PPh2-P,P)2(C,N:C,N)] (C,N:C,N = bis(N-2,3,4-trimethoxybenzylidene)-4,4'-sulfonyldianiline or -4,4'-oxydianiline) can undergo a spontaneous slow chelate-to-bridging diphosphane coordination shift in solution. Following this strategy a tailor-made synthetic procedure was devised that culminates in isolation of double A-frame tetranuclear palladium complexes.

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.

The potential of 15-crown-5 ethers to link large cations, such as potassium, is limited by the quasi-parallel arrangement of two oxygen donor moieties upon appropriate orientation of the corresponding ether-ring-containing molecules. Substrates bearing the two crown ethers that are capable of achieving such coordination are hitherto unknown. The synthesis and isolation of a tailor-made dinuclear palladacycle bearing 15-crown-5 ether rings on the metallated phenyls offers such a possibility, providing the adequate environment for the formation of the sandwiched [K(metallacycle-15-crown-5)2] moiety. This synthetic strategy also culminates in the isolation of the first palladacycle able to entrap a potassium cation through bonding to two 15-crown-5 ether rings in a single molecule.

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.

Treatment of thiosemicarbazones (R 1C 6H 4)C(H)NN(H)C(S)NHR 2 [R 1,R 2: 4-Me,H (a); 4-Me,Me (b); 4-Me,Et (c); 2-Me,H (d); 2-Me,Me (e); 2-Me,Et (f)] with cis-[PtMe 2(cod)] afforded the tetranuclear platinum(II) compounds [Pt{(R 1C 6H 3)C(H)NNC(S)NHR 2}] 4 (1a-1f) with the ligand as terdentate [C,N,S] after C-H activation and NH deprotonation. The reaction of 1a-1f with PPh 3 in 1:4 M ratio gave the mononuclear compounds [Pt{(R 1C 6H 3)C(H)NNC(S)NHR 2}(PPh 3)] (2a-2f). Treatment of 1a-1f with large-bite diphosphines Ph 2P(CH 2) nPPh 2 (n = 2, dppe; n = 3, dppp; n = 4, dppb) afforded the dinuclear compounds [{Pt[(R 1C 6H 3)C(H)N-N = C(S)NHR 2]} 2{μ-Ph 2P(CH 2) nPPh 2}], (3a-3f, 4a-4f, 5a-5f), with the diphosphine in a bridging mode. Similar reactions with the short-bite diphosphines Ph 2PCH 2PPh 2 (dppm) and Ph 2PC(CH 2)PPh 2 (vdpp) yielded the mononuclear compounds [Pt{(R 1C 6H 3)C(H)NNC(S)NHR 2}(Ph 2PR 3PPh 2-P)] (R 3 = CH 2, 6a-6f; R 3 = C = CH 2, 7a-7f) with the diphosphine in a monodentate coordination. Treatment of 1a-1f with [W(CO) 5(Ph 2CH 2PPh 2)] gave the heterodinuclear species [{Pt[(R 1C 6H 3)C(H)NNC(S)NHR 2]} {Ph 2CH 2PPh 2W(CO) 5}] (8a-8f). The molecular structures of compounds 3e and 5c have been determined by X-ray crystal structure analysis. © 2012 Elsevier Ltd. All rights reserved.

Reaction of the Schiff base ligands CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)═NR] (R = 2,4,6-Me3C6H2, a; R = Cy, b) derived from the 1,2-disubstituted formylferrocene CpFe[(CHO){C(H)O(CH2)3O}-η5-C5H3] 1, with Li2[PdCl4] in methanol at room temperature for 48 h, gave the chlorine-bridged complexes [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)═NR]}(Cl)]2, 1a and 1b, after C–H activation of the cyclopentadienyl ring bearing the cyclic acetal. The reactions of 1a and 1b with the Ph2P(CH2)nPPh2 diphosphines in a 1:2 ratio, plus addition of ammonium hexafluorophosphate, gave the dinucelar compounds [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)═NR]}-(Ph2P(CH2)nPPh2-P,P)][PF6] 2a, 3a and 2b, 3b with the diphosphine in a chelating mode, as 1:1 electrolytes. Treatment of the latter with aqueous acetic acid gave the corresponding functionalized compounds with transformation of the 1,3-dioxane ring into a formyl group on the metalated ring, 4a, 5a and 4b, 5b.The Schiff base condensation reaction of 5b with 2-(methylthio)aniline in refluxing chlorofo...

Reaction of the thiosemicarbazones 3-FC6H4C(Me)NN(H) C(S)NHME a, 4-FC6H4C(Me)NN(H)C(S)NHEt b, and 2-BrC 6H4C(Me)NN(H)C(S)NHPh c, with potassium tetrachloropalladate(II) in ethanol, lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complexes [Pd{3-FC6H3C(Me)NNC(S)NHMe}] 4 1a, [Pd{4-FC6H3C(Me)NNC-(S)NHEt}]4 1b, and [Pd{2-BrC6H3C(Me)NNC(S)NHPh}]4 1c. Reaction of 1a-c with the diphosphines Ph2P(CH2) nPPh2 dppm (n = 1), dppe (n = 2), dppp (n = 3), dppb (n = 4) or Ph2PCHCHPPh2 trans-dppe, in a 1:2 molar ratio gave the dinuclear phosphine-bridged complexes [(Pd{XC6H 3C(Me)NNC(S)NHR})2(μ-Ph2P(CH 2)nPPh2)] 2a-c, 3a-c, 4a-c, 5a-c (n = 1-4) and [(Pd{XC6H3C(Me)NNC(S)NHR})2(μ-Ph 2PCHCH-PPh2)] 6a-c. Treatment of 1a-c with PPh 2CH2PPh2, dppm, in a 1:4 molar ratio gave the mononuclear cyclometallated complexes [Pd{XC6H3C(Me)NNC(S) NHR}-(Ph2PCH2PPh2-P)] 7a-c; however, the diphosphines with n ≥ 2 failed to give the analogous reaction. The molecular structures of 1a, 1b and 3c have been determined by X-ray diffraction analysis and the intra- and intermolecular interactions are discussed. © 2011 Elsevier Ltd. All rights reserved.

Treatment of bimetallic palladacycles with silver perchlorate, followed by reaction with tertiary diphosphanes or diphenyl-2-pyridylphosphane gave novel dipalladium compounds with chelating [C,N,S], bridging [P,P], and chelating [P,P] or [P,N] ligands, as appropriate. The short-chain diphenyl-2- pyridylphosphane ligand forms stable four-membered P-N chelates, which display S-Pd-P and N-Pd-P trans geometries. The Pd-Cl bonds are nonreactive towards displacement by the [P,P] or [P,N] ligands, even in the case of strong chelating diphosphanes. New bimetallic palladacycles with bridging [P,P] and chelating [P,P], [P,N], and [C,N,S] donors are reported. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA.

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).

Treatment of 4-MeOC6H4C(Me)═NN(H)C(═S)NHMe (1), with potassium tetrachloropalladate gave the tetranuclear compound [Pd{4-MeOC6H3C(Me)═NN═C(S)NHMe}]4 (2), with the ligand as terdendate [C,N,S]. Reaction of 2 with the diphosphines Ph2PCH2PPh2 (dppm), Ph2PC(═CH2)PPh2 (vdpp), and Ph2PC(CH2)2PPh2 (dpcp) gave the mononuclear complexes [Pd{4-MeOC6H3C(Me)═NN═C(S)NHMe}(L)] (L = dppm-P, 3; dpcp-P, 4; vdpp-P, 5) with the diphosphine ligand binding in a monodentate fashion. Compounds 3−5 may bond systematically to a second metal atom, palladium or platinum, through the noncoordinated phosphorus atom and the sulfur atom of the thiosemicarbazone moiety to give the dinuclear compounds 6−10, thus behaving as bidentate P,S-palladacycle metaloligands. All the compounds have been characterized by elemental analysis, and by IR and NMR spectroscopy; and the crystal and molecular structures of 1, 2, 6−10 have been determined by X-ray crystallography. Inter- and intramolecular hydrogen bonding in the solid results in crystal se...

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 thiosemicarbazones (OC4H3)C(Me)= NN(H)C(=S)NHR (R: Me, a; Et, b) with [cis-PtMe2(cod)] afforded the tetranuclear compounds [Pt{(OC4H2)C(Me)=NN=C(S)NHR}] 4 (R: Me, 1a; Et, 1b). The reaction of la and lb with triphenylphosphine in 1:4 molar ratio gave rise to the mononuclear compounds [Pt{(OC4H2)C(Me)=NN=C(S)NHR)(PPh3)] (2a, 2b). Treatment of la and lb with large-bite diphosphines Ph2P(CH 2)nPPh2 (n = 2, dppe; n = 3, dppp; n = 4, dppb) afforded the dinuclear compounds [{Pt[(OC4H2)C(Me) = NN=C(S)NHR]}2{μ-Ph2P(CH2) nPPh2}], (3a-5a, 3b-5b), with the diphosphine in a bridging mode. Similar reactions with the short-bite diphosphines Ph 2PCH2PPh2 (dppm) and Ph2PC(=CH 2)PPh2 (vdpp) yielded the mononuclear compounds [Pt {(OC4H2)C(Me)=NN=C(S)NHR}-(Ph2PCH 2PPh2-P)] (6a, 6b) and [Pt{(OC4H 2)C(Me)=NN=C(S)NHR}(Ph2P-C(= CH2)PPh 2-P)] (7a, 7b) with the diphosphine in a monodentate coordination. Treatment of la and lb with [W(CO)5(Ph2CH 2PPh2)] gave the novel heterodinuclear species [{Pt[(OC4H2)C(Me)=NN= C(S)NHR]}[W(CO)5(Ph 2CH2PPh2-P)}] (8a, 8b), which could also be synthesized by reaction of 6a and 6b with [W(CO)5(THF)], 1H, 31P-{1H} and 13C-{1H} NMR and IR data are given. The crystal structure of compound 3b has been determined by X-ray crystallography. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

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 the thiosemicarbazone 2-FC6H4C(Me)= NN(H)C(=S)NHPh, a, with palladium(II) acetate in acetic acid, or with lithium tetrachloropalladate(II) in methanol, gave the tetranuclear cyclometallated complex [Pd{2-FC6H3C(Me)=NN= C(S)NHPh}]4 (1a). Reaction of 1a with the diphosphines Ph2P(CH2) 2PPh2 (dppe), Ph2PCH=CHPPh2 (trans-dpe) Ph2P(CH2)3Ph2 (dppp) or Ph2P(CH2)4Ph2 (dppb) in a 1:2 molar ratio gave the dinuclear cyclometallated complexes [(Pd{2-FC6H 3C(Me)=NN=C(S)NHPh})2(μ-Ph2P(CH 2)nPPh2)], (n = 2, 2a; 3, 4a; 4, 5a) and [(Pd{2-FC6H3C(Me)=NN=C(S)NHPh})2(μ-Ph 2PCH=CHPPh2)], (3a). The X-ray crystal structure of ligand a and of complex 2a are described. The structure of complex 2a shows the palladium atom is bonded to four different donor atoms: C, N, S and P. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.

Treatment of the 1-ferrocenylethanone thiosemicarbazone ligands (η5-C5H5)Fe(η5-C5H4)C(Me)=NN(H)C(=S)NHR [R = H (a), Me (b)] with K2[PdCl4] gave the novel heterometallic octanuclear palladium(II) compounds [Pd{(η5-C5H5)Fe(η5-C5H3)C(Me)=NN=C(S)NHR}]4 [R = H (1a), Me (1b)] as tetramers, after deprotonation of the NH group, with the ligands acting as terdentate donors through the [C,N,S] atoms. Treatment with nucleophiles cleaves the tetrameric clusters giving compounds in which splitting only of the Pd−Sbridging bonds has occurred. The strength of the Pd−Schelating bond hinders its cleavage. Thus, treatment of 1a or 1b with Ph2P(CH2)nPPh2 [n = 2 (dppe), 3 (dppp), 4 (dppb)] in a 1:2 molar ratio gave the tetranuclear species 2a−4a and 2b−4b, respectively, and treatment with PPh2R gave the dinuclear compounds 5a−7a and 5b−6b [R = Ph (5a, 5b), Et (6a, 6b), Me (7a)]. The complexes described are the first fully characterized cyclometallated palladium(II) complexes with 1-ferrocenylethanone thiosemicarbazone ligands. The crystal and molecular structure of compound 5b have been determined by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Treatment of the Schiff-base ligands C 6 H 5 C(H)=C(R)C(H)=NCy (R=H, a; R=Me, b) with Pd(OAc) 2 gave the acetato-bridged dinuclear compounds [Pd{C 6 H 5 C=C(R)C(H)=NCy}(O 2 CMe)] 2 (R=H, 1a; R=Me, 1b) after C-H activation of the aliphatic carbon atom. Reaction of 1a and 1b with aqueous sodium chloride gave the dinuclear chloro-bridged compounds [Pd{C 6 H 5 C=C(R)C(H)=NCy}(X)] 2 (R=H, 2a; R=Me, 2b), which could also be prepared by treatment of the ligands with Li 2 [PdCl 4 ] in methanol. Reaction of 1a with aqueous sodium bromide or iodide gave the halide-bridged species [Pd{C 6 H 5 C=C(H)C(H)=NCy}(X)] 2 (X=Br, 3a; X=I, 4a). Treatment of 1a and 1b with Tl(acac), Tl(C 5 H 5 ) or PPh 3 , as appropriate, gave the mononuclear complexes [Pd{C 6 H 5 C=C(R)C(H)=NCy}(acac)], (R=H, 5a; R=Me, 3b) [Pd{C 6 H 5 C=C(H)C(Me)=NCy}(C 5 H 5 )] (4b) and [Pd{C 6 H 5 C=C(H)C(Me)=NCy}(PPh 3 )] (5b). © 2002 Elsevier Science B.V. All rights reserved.

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.

Reaction of the Schiff base ligand 1,3-[2,3,4-(MeO)3C6H2C(H)NCH2]2C6H4 (1) with palladium(II) acetate in toluene gave the doubly cyclometalated complex [1,3-{Pd[2,3,4-(MeO)3C6HC(H)NCH2](μ-O2CMe)}2C...

Treatment of the Schiff base 2-ClC6H4C(H)NCH2CH2SMe, 1, with palladium(II) acetate in dry toluene gave the mononuclear cyclometallated complex [Pd{2-ClC6H3C(H)NCH2CH2SMe}(O2CMe)], 2. Reaction of 2 with aqueous sodium chloride gave [Pd{2-ClC6H3C(H)NCH2CH2SMe}(Cl)], 3, after a metathesis reaction. The X-ray crystal structure of 3 was determined and shows that the palladium atom is bonded to four different donor atoms: C, N, S and Cl. Treatment of 3 with triphenylphosphine in acetone gave the mononuclear cyclometallated complex [Pd{2-ClC6H3C(H)NCH2CH2SMe}(Cl)(PPh3)] with cleavage of the Pd–S bond. However, treatment of 3 with silver triflate and triphenylphosphine gave [Pd{2-ClC6H3C(H)NCH2CH2SMe}(PPh3)][CF3SO3], 10, in which the Pd–S bond is retained. Reaction of 3 with the diphosphines dppm, dppb or dppf in a 2 : 1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-ClC6H3C(H)NCH2CH2SMe](Cl)}2{μ-Ph2P(CH2)nPPh2}], (n=1, 5; n=4, 6), and [{Pd[2-ClC6H3C(H)NCH2CH2SMe](Cl)}2(μ-Ph2PC5H4FeC5H4PPh2)], 7. Treatment of 3 with dppb in a 2 : 1 molar ratio and AgCF3SO3 gave the dinuclear cyclometallated complex [{Pd[2-ClC6H3C(H)NCH2CH2SMe]}2{μ-Ph2P(CH2)4PPh2}][CF3SO3]2, 11, which was characterized by X-ray crystal structure analysis. Reaction of 3 with dppe in a 1 : 1 molar ratio and sodium perchlorate gave the mononuclear complex [Pd{2-ClC6H3C(H)NCH2CH2SMe}{Ph2P(CH2)2PPh2-P,P}][ClO4], 8. Treatment of 3 with bis(2-diphenylphosphinoethyl)phenylphosphine in a 1 : 1 molar ratio, followed by treatment with sodium perchlorate gave [Pd{2-ClC6H3C(H)NCH2CH2SMe}{(Ph2PCH2CH2)2PPh-P,P,P}][ClO4], 9, in which the triphosphine is bonded to the palladium atom through the three phosphorus atoms.

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.

X-ray diffraction studies show that the title cyclometallated compounds show each palladium atom C,N-bonded to a deprotonated Schiff base ligand. The molecular configuration is a dimeric form of the anti isomer with the cyclopalladated moieites in an open-book' arrangement linked by two acetate bridging ligands.

The palladium(II) compound [Pd{3,4-(MeO)2C6H2C(H)NCy}{(Ph2PCH2CH2)2PPh-P,P,P}][PF6] was synthesized and characterized by elemental analysis (C, H, N) and by 1H and 31P{1H} NMR spectroscopy in CDCl3 and 31P{1H} solid-state NMR spectroscopy. The molecular structure was determined by X-ray crystallography, showing it to be the first pentacoordinated cyclometalated palladium(II) complex.