Water-soluble phosphines

Covalent Modification of Nucleobases using Water-Soluble Palladium Catalysts

Nucleosides represent one of the key building blocks of biochemistry. There is significant interest in the synthesis of nucleoside-derived materials for applications as probes, biochemical models, and pharmaceuticals. Palladium-catalyzed cross-coupling reactions are effective methods for making covalent modification of carbon and nitrogen sites on nucleobases under mild conditions. Water-soluble catalysts derived from palladium and hydrophilic ligands, such as tris(3-sulfonatophenyl)phosphine trisodium (TPPTS), are efficient catalysts for a range of coupling reactions of unprotected halonucleosides. Over the past two decades, these methods have been extended to direct functionalization of halonucleotides, as well as RNA and DNA oligonucleotides (ONs) containing halogenated bases. These methods can be run under biocompatible conditions, including examples of Suzuki coupling of modified DNA in whole cells and tissue samples. In this account, development of this methodology by our group and others is highlighted along with the extension of these catalyst systems to modification of nucleotides and ONs.

Coordination behaviour of a hybrid phosphinoguanidine ligand

A triphenylphosphine derivative equipped with a guanidine substituent in the ortho position readily forms P,N-chelate complexes with Pd(ii) and Pt(ii); however, the coordination of the guanidine moiety can be blocked by protonation.

The protonation state governs the coordination of phosphinoferrocene guanidines

Compared to phosphines with guanidinium tags, studied as polar ligands for aqueous catalysis, their counterparts bearing guanidine substituents received only limited attention. This contribution focuses on the coordination of phosphinoferrocene guanidine Ph₂PfcNC(NHiPr)₂ (1iPr, fc = ferrocene-1,1'-diyl) as a hybrid, P,N-donor ligand to Group 10 metals. In its native state, 1iPr coordinated as a P,N-chelating ligand, affording [M(X)(Y)(1iPr-κ²P,N)] (M/X/Y = Pd/Cl/Cl, Pd/Br/4-C₆H₄CN, Pt/Cl/Cl; the corresponding Ni(II) complex was not isolated). While [PdCl₂(1iPr-κ²P,N)] converted into [PdCl(1iPr-κ³Fe,P,N)]⁺ species with Fe-Pd interaction, upon chloride removal, the analogous Pt(II) complex dimerised into [Pt₂(μ-Cl)₂(1iPr-κ²P,N)₂]²⁺. Deprotonation of [PdCl₂(1iPr-κ²P,N)] produced a unique, doubly chelating phosphinoguanidinate complex [PdCl{(1iPr-H)-κ³P,N,N'}], which was smoothly converted into [Pd(MeCN){(1iPr-H)-κ³P,N,N'}][SbF₆]. The latter, a convenient starting material for substitution reactions, was used to prepare either [Pd(L){(1iPr-H)-κ³P,N,N'}][SbF₆] (L = 4-(dimethylamino)pyridine and 2-phenylpyridine), by simple substitution, or the hydroxide and acetylacetonate (acac) complexes, [Pd₂(μ-OH)₂(1iPr-κ²P,N)₂][SbF₆]₂ and [Pd(acac)(1iPr-κ²P,N)][SbF₆], by substitution with concomitant proton transfer. In contrast, protonation of the guanidine moiety prevented its coordination, as shown in reactions of the salts (1iPrH)Cl and (1iPrH)[SbF₆]. Depending on the metal-to-ligand ratio, adding (1iPrH)[SbF₆] to [PdCl₂(MeCN)₂] produced [Pd₂Cl₂(μ-Cl)₂(1iPrH-κP)₂][SbF₆]₂ or [PdCl₂(1iPrH-κP)₂][SbF₆]₂. Analogous reactions involving (1iPrH)Cl were more complicated due to competing coordination of the chloride anion, leading to (in addition to other compounds) the zwitterionic complex [PdCl₃(1iPrH-κP)], which was alternatively obtained by selective protonation of [PdCl₂(1iPr-κ²P,N)] with HCl. Apparently, the protonation state of the guanidine moiety controls the coordination behaviour of phosphinoferrocene guanidines.

Synthesis and study of Fe → Pd interactions in unsymmetric Pd(ii) complexes with phosphinoferrocene guanidine ligands

Readily available phosphinoferrocene guanidines coordinate Pd(ii) as P,N-chelating or κ3P,N,Fe-bound ligands. As the latter, they give rise to the first donor-asymmetric complexes featuring Fe-Pd dative bonds, which were studied using direct (spectroscopic and electrochemical) methods and theoretical (DFT) approaches.

Superagonist, Full Agonist, Partial Agonist, and Antagonist Actions of Arylguanidines at 5-Hydroxytryptamine-3 (5-HT3) Subunit A Receptors

Introduction of minor variations to the substitution pattern of arylguanidine 5-hydroxytryptamine-3 (5-HT₃) receptor ligands resulted in a broad spectrum of functionally-active ligands from antagonist to superagonist. For example, (i) introduction of an additional Cl-substituent(s) to our lead full agonist N-(3-chlorophenyl)guanidine (mCPG, 2; efficacy % = 106) yielded superagonists 7-9 (efficacy % = 186, 139, and 129, respectively), (ii) a positional isomer of 2, p-Cl analog 11, displayed partial agonist actions (efficacy % = 12), and (iii) replacing the halogen atom at the meta or para position with an electron donating OCH₃ group or a stronger electron withdrawing (i.e., CF₃) group resulted in antagonists 13-16. We posit based on combined mutagenesis, crystallographic, and computational analyses that for the 5-HT₃ receptor, the arylguanidines that are better able to simultaneously engage the primary and complementary subunits, thus keeping them in close proximity, have greater agonist character while those that are deficient in this ability are antagonists.

Diphosphine capsules for transition-metal encapsulation

Self-assembly and characterization of novel heterodimeric diphosphine capsules formed by multiple ionic interactions and composed of one tetracationic diphosphine ligand and one complementary tetraanionic calix[4]arene are described. Encapsulation of a palladium atom within a diphosphine capsule is achieved successfully by using the metal complex of the tetracationic diphosphine ligand for the assembly process. In this templated approach to metal encapsulation, the transition-metal complex is an integrated part of the capsule with the transition metal located inside the capsule and is not involved in the assembly process. We present two approaches for capsule assembly by mixing solutions of the precharged building blocks in methanol and mixing solutions of the neutral building blocks in methanol. The scope of the diphosphine capsules and the metallodiphosphine capsules is easily extended by applying tetracationic diphosphine ligands with different backbones (ethylene, diphenyl ether, and xanthene) and cationic binding motifs (p-C(6)H(4)-CH(2)-ammonium, m-C(6)H(4)-ammonium, and m-C(6)H(4)-guanidinium). These tetracationic building blocks with different flexibilities and shapes readily associate into capsules with the proper capsular structure, as is indicated by (1)H NMR spectroscopy, 1D NOESY, ESI-MS, and modeling studies.

Organometallic catalysts in synthetic organic chemistry: From reactions in aqueous media to gold catalysis

Water has attracted significant attention as an alternative solvent for transition-metal-catalyzed reactions. The use of water as solvent allows simplified procedures for separation of the catalyst from the products and recycling of the catalyst. Water is an inexpensive reagent for the formation of oxygen-containing products such as alcohols. The use of water as a medium for promoting organometallic and organic reactions is also of great potential. This chapter will focus on old and recent developments in the design and applications of some catalytic reactions using aqueous-phase Pd, Rh, Pt, and Au complexes.

Unsymmetrical diaryl sulfones through palladium-catalyzed coupling of aryl iodides and arenesulfinates

[reaction: see text] The palladium-catalyzed coupling of aryl iodides and arenesulfinates provides a simple and extremely efficient new route to unsymmetrical diaryl sulfones, usually isolated in high yield. The reaction tolerates a variety of functionalized aryl iodides, including those containing ether, ester, and nitro groups. The best results have been obtained by using Pd(2)(dba)(3), Xantphos, Cs(2)CO(3), and (n)Bu(4)NCl in toluene at 80 degrees C.

Water-soluble phosphines. 17.(1) novel water-soluble secondary and tertiary phosphines with disulfonated 1,1'-biphenyl backbones and dibenzophosphole moieties

Reaction of 2,2'-difluoro-1,1'-biphenyl with chlorosulfonic acid and subsequent hydrolysis followed by neutralization with potassium or sodium hydroxide affords disodium or dipotassium 5,5'-disulfonato-2,2'-difluoro-1,1'-biphenyl (1a, 1b). On treatment of 1b with diphenyl- or phenylphosphine in the superbasic medium DMSO/KOH, phosphine ligand 2 or 3 with a disulfonated 1,1'-biphenyl backbone or a dibenzophosphole moiety is formed. The structure of the oxide of 5-phenyldibenzophosphole 3, which crystallizes as 4.2.5H(2)O in the monoclinic space group P2(1)/n with a = 13.799(3) A, b = 19.246(4) A, c = 17.764(4) A, beta = 105.63(3) degrees, and Z = 4, has been determined by X-ray analysis. Nucleophilic phosphination of 1a with NaPH(2) in liquid ammonia yields the sodium phosphide 5a which on protonation gives the water-soluble 5H-dibenzophosphole 5. Reaction of 1b with PH(3) in the superbasic medium DMSO/KOtBu affords 5b in addition to the oxidation product 6a. On oxidation of 5a or 5b with H(2)O(2), the sodium or potassium salts of the sulfonated phosphinic acids 6a or 6b, respectively, are formed. Alkylation of the sodium dibenzophospholide 5a with 2,2'-bis(chloromethyl)-1,1'-biphenyl or 1,4-di-O-p-toluenesulfonyl-2,3-O-isopropylidene-D-threitol yields the chiral water-soluble bidentate phosphine ligands 8 and 9, respectively.