Study of the Reactivity of the [(PE¹CE²P)Ni(II)] (E¹, E² = O, S) Pincer System with Acetonitrile and Base: Formation of Cyanomethyl and Amidocrotononitrile Complexes versus Ligand Decomposition by P–S Bond Activation

Abstract

Nickel(II) chloride complexes with PE 1 CE 2 P (E = O, S) pincer ligands were used as precursors for the generation of cyanomethyl complexes in order to investigate the influence of variations (O vs S) in the side arms of the ligands on reactivity and stability of such compounds. In this regard, five hitherto unknown Ni(II) compounds were synthesized and fully characterized. Reaction of the Ni(II) chloride complex [( iPr POCSP iPr )NiCl] (2-Cl) with 1 equiv of base and nitrile furnishes the cyanomethyl complex [( iPr POCSP iPr )NiCH 2 CN] (2-CM). Increase of the amount of base and nitrile results in the formation of 3-amidocrotononitrile complexes [( iPr POCOP iPr )NiNHC(CH 3 )CHCN] (1-ACN) and [( iPr POCSP iPr )NiNHC(CH 3 )CHCN] (2-ACN). In contrast, similar reactions of the bis(thiophosphinite) complex 3-Cl resulted in formation of a tetranuclear Ni cluster (4) or a dinuclear 1,3-dithiolate-bridged PSCSP complex 5 by unexpected cleavage of P−S bonds of the pincer ligand.

Assembly of metallo-macrocycles through reductive C–C coupling of alkylnitriles by an Mg–Mg-bonded compound

“…In all of the products, the coupled amido-ene-nitrile units adopt the E conformation about the CvC bond, possibly resulting from the steric repulsion of the long alkyl chains that span above and below the macrocycle. In previous examples, however, most of the (dinuclear bridging) complexes show the Z form, and there are only several compounds that adopt the E conformation 43,48,49 The bond parameters of the bridging units in 2-4 are comparable with those in the Li, 50,51 Sr, 17 Y, 42,52 Re, 53 Sm, 54 and Yb 55 complexes with (Z)crotonitrileamido ligands, and compounds of Zr, 48 Rh 49 and Ni 43 with (E) crotonitrileamido isomer. On the basis of previous reports 17,43,52 and mechanism studies, the formation of 2-4 can be explained by a reductive α-H elimination and subsequent C-C coupling through insertion of the second nitrile, to yield possible intermediates with the imido-nitrile fragments NuCCHRC(CH 2 R)vN − .…”

“…In previous examples, however, most of the (dinuclear bridging) complexes show the Z form, and there are only several compounds that adopt the E conformation 43,48,49 The bond parameters of the bridging units in 2-4 are comparable with those in the Li, 50,51 Sr, 17 Y, 42,52 Re, 53 Sm, 54 and Yb 55 complexes with (Z)crotonitrileamido ligands, and compounds of Zr, 48 Rh 49 and Ni 43 with (E) crotonitrileamido isomer. On the basis of previous reports 17,43,52 and mechanism studies, the formation of 2-4 can be explained by a reductive α-H elimination and subsequent C-C coupling through insertion of the second nitrile, to yield possible intermediates with the imido-nitrile fragments NuCCHRC(CH 2 R)vN − . This is followed by a 1,3-H shift (from carbon to nitrogen atom) to give the final products containing NuCC(R)vC(CH 2 R)-NH − moiety.…”

“…Similar phenomena have been reported before to yield either di-or mononuclear complexes. [39][40][41][42][43] For example, the reactions of some yttrium complexes with acetonitrile occurred through C-H deprotonation and C-C coupling, yielding dinuclear complexes with the coupled moieties of two acetonitrile molecules, µ-{((N,N′)-N(H) C(Me)vC(H)CuN)}. 42 .…”

“…17 In some cases, the resulted amidocrotononitrile does not act as a bridging ligand, but coordinates via the amido nitrogen to metal center. 43 In addition, couplings of three or more nitrile molecules are also known. [35][36][37] Nevertheless, as mentioned above, reactions with less active aliphatic nitriles (such as alkylnitriles in the current work) has not been reported so far.…”

Hybrid POCZP Aryl Pincer Metal Complexes and their Catalytic Applications

“…In a similar way, reaction of 1b with LiCH 2 CN afforded the cyanomethyl derivative 1e (Scheme 6). [ 41 ] However, when the reaction is carried out in the presence of an excess of n BuLi an amidocrotononitrile 1f was formed and isolated. It is noteworthy that having a 3‐amidocrotononitrile group as anionic ligand is a rare event; and only a few of such cases are known in the literature.…”