ChemInform Abstract: 1,8‐Bis(diphenylphosphino)anthracene and Metal Complexes.

Abstract

The title compound 4 was synthesized from dipotassium 1,8-anthracenedisulfonate (9) and potassium diphenylphosphide (Ph,PK). On reaction of 4 with nickel(I1) chloride and bis-(benzonitrile)palladium(II) chloride, cyclometallation of the C -H bond in anthracene 9-position led to the square-planar chelate complexes 11 and 13, respectively. In the case of the palladium complex 13, the cyclometallated structure was proved by X-ray structure analysis. Treatment with aqueous potassium cyanide did not remove nickel from 11, but converted 11 into 12 by substitution of chloride with cyanide, demonstrating the high stability of these cyclornetallated chelate complexes.Generally, bidentate phosphine ligands such as 1,2-bis(dipheny1phosphino)ethane (1) or 1,2-bis(diphenylphosphino)benzene (3) coordinate metals to form preferably monometallic chelate complexes. If both phosphorus centres have mutual geometries unfavourable for the formation of monometallic chelate complexes, bimetallic complexes can also be obtained. For example, in the case of 1,2-bis(diphenylphosphino)methane (2) a monometallic chelate complex (involving the formation of a four-membered ring) is disfavoured, so that under certain conditions the bidentate ligand coordinates two metals2). Another approach to form bimetallic complexes is the synthesis of bidentate phosphines in which rigid carbon skeletons are used to arrange two phosphorus centres at distances too long to coordinate simultaneously one metal nucleus, but short enough to bring two coordinated metals in close proximity. Such homo-or heterobinuclear metal complexes might bear interesting features and new potentials, especially with respect to catalytic processes ' ).In pursuing this concept we have synthesized 1,8-bis(diphenylphosphin0)anthracene (4) and studied in preliminary experiments its behaviour as a ligand in metal complexation. Thereby monometallic nickel(I1) and palladium(I1) chelate complexes of 4 have been obtained, the formation of which has not been expected at first sight. While the intramolecular phosphorus -phosphorus distance of about 5 A still is reasonable for chelate formation, the phosphorus valence angle and especially the steric requirements of the anthracene 9-hydrogen are unfavourable. However, if simultaneously with coordination to both phosphorus centres the metal is inserted into the C-H bond in anthracene 9-position, monometallic cyclometallated chelate complexes become feasible4).The synthesis of 4 has first been attempted starting from 1,8-dichl~roanthracene'~ (5). However, it has not been possible to convert 5 by twofold metallation into either the dilithium compound 6 or the di-Grignard compound 7 from both of which 4 should have been accessible by the successive reaction with chlorodiphenylphosphine. The reaction of 5 with lithium diphenylphosphide (Ph,PLi)6) has given 4 only in yields below 2%. Anticipating higher reactivity, 1,8-dibromoanthracene (8, m.p. 162-165 "C) has been synthesized from dipotassium 9,lO-anthraquinone-1 $-disulfonate ' ) by reaction wit...

C–H Nickelation of Aryl Phosphinites: Mechanistic Aspects

“…A search of the literature revealed that most cyclonickelated complexes accessible via C−H nickelation are stabilized by pincer-type ligands. 6 Our experience with the facile C−H nickelation of POCOP-type pincer ligands featuring aryl and alkyl phosphinite donor moieties 7 encouraged us to test the reactivities of substrates bearing a single phosphinite DG. Initial tests showed that alkyl phosphinites were insufficiently reactive, whereas aryl phosphinites underwent relatively facile C−H nickelation.…”

XL-Xantphos: Design and Synthesis of a Mechanistic Probe of Xantphos O-Coordination in Catalytic Reactions

“…This spacer design is analogous to that used in the related family of diphosphine ligands based on 1,8-bis­( p -(diphenylphosphino)­phenyl)­anthracene ( L1 ), which were designed to be selective for trans chelation. In this particular case, the phenyl spacer in L1 excludes the possibility of C–H activation that results in formation of P–C–P pincer complexes with L2 . A related, electron-rich ligand with a 1,3-phenyl spacer, L3 , has also been described and can support both cis and trans coordination modes …”

Hydroamination of Aromatic Alkynes to Imines Catalyzed by Pd(II)–Anthraphos Complexes

“…Palladium complexes [Pd­(Anthraphos Ph )­Cl] ( 4 , Ph = phenyl) and [Pd­(Anthraphos Xyl )­Cl] ( 5 , Xyl = 3,5-dimethylphenyl) were prepared by following modified reported procedures in the individual steps, as described in Scheme . ,,, …”

“…A prototypical tridentate example is the Anthraphos ligand, resulting in a large P−Pd−P angle of 166.2 (1)°. 52,53 Moreover, the palladium(II) Anthraphos system has demonstrated high efficiency for a broad range of reactions such as the formation of CC double bonds in allylation, electrophilic substitution, or dehydrogenation reactions. 53−60 However, they have yet to be studied for hydroamination reactions.…”

“…However, to the best of our knowledge, palladium pincer complexes have not been reported for the intermolecular hydroamination of alkynes. A prototypical tridentate example is the Anthraphos ligand, resulting in a large P–Pd–P angle of 166.2 (1)°. , Moreover, the palladium­(II) Anthraphos system has demonstrated high efficiency for a broad range of reactions such as the formation of CC double bonds in allylation, electrophilic substitution, or dehydrogenation reactions. − However, they have yet to be studied for hydroamination reactions. The present study aims at fulfilling this gap and discloses the synthesis and catalytic activity of palladium­(II) complexes supported by Anthraphos ligands.…”