Nickel complex isoelectronic

Isoelectronic with nickel carbonyl are the anions, Ni(CN)44- and Pd(CN)44-, which are obtained as their potassium salts by reduction of the corresponding cyanides of oxidation state +2 with potassium in liquid ammonia (32, 65, 186). The infrared spectrum of the nickel complex has been reported (67) to show only one band at 1985 cm-1, in the triple-bond... 

Experimentally, it has been shown that the reductive elimination of R2 is easier for a nickel complex than for the isoelectronic palladium-containing species. This result may be readily understood from the correlation diagram in Figure 4.12. 

Cyclobutadiene complexes are also relatively stable, but many of them undergo decomposition in air. Such complexes are formed by metals of groups 4-10 containing central atoms of d" -d electronic structures. Recently, the first biscyclobutadiene compound was obtained it is the nickel complex [Ni(C4Ph4)2] which is isoelectronic with ferrocene, Fecp2- The molecular orbital scheme for this compound is presented in Figure 8.8. 

Alkynyl complexes, which contain the grouping M—C=CR, are often more stable than the corresponding alkyls and aryls. An example is the nickel complex (Et3P)2Ni(C=CPh)2, wtiich melts at 149-15rc without decomposition. Alkynyl complexes are formally similar to metal cyanides and metal carbonyls. The species C=CR, CN and CO are all isoelectronic and presumably bond to a transition metal in a similar manner. All three ligands would be expected to possess both a-donor and ir-acceptor... 

Beyond palladium, it has recently been shown that isoelectronic metal complexes based on nickel and platinum are active catalysts for diyne reductive cyclization. While the stoichiometric reaction of nickel(O) complexes with non-conjugated diynes represents a robust area of research,8 only one example of nickel-catalyzed diyne reductive cyclization, which involves the hydrosilylative cyclization of 1,7-diynes to afford 1,2-dialkylidenecyclohexanes appears in the literature.7 The reductive cyclization of unsubstituted 1,7-diyne 53a illustrates the ability of this catalyst system to deliver cyclic Z-vinylsilanes in good yield with excellent control of alkene geometry. Cationic platinum catalysts, generated in situ from (phen)Pt(Me)2 and B(C6F5)3, are also excellent catalysts for highly Z-selective reductive cyclization of 1,6-diynes, as demonstrated by the cyclization of 1,6-diyne 54a.72 The related platinum bis(imine) complex [PhN=C(Me)C(Me)N=Ph]2Pt(Me)2 also catalyzes diyne hydrosilylation-cyclization (Scheme 35).72a... 

All of these metal complexes are isoelectronic and isostructural with each other. Upon coordination of the carbon monoxide to the nickel(O) centre, the metal ion acquires negative charge. The carbon monoxide ligand possesses empty 7r -orbitals, and back-donation from the metal to the ligand reduces the electron density on the metal. 

The structures of the isoelectronic hydridocarbonyls H2Fe(CO)4 and HCo(CO)4 were the central theme of numerous studies over a period of many years after their discovery by Hieber. Because of their very similar physical characteristics, these complexes were considered to be pseudo nickel tetracarbonyls (H2Fe = HCo = Ni) in which, even then, the... 

K2[Fe(NO)2(CN)2]. My former co-worker R. Nast (83) showed that the reaction of carbon monoxide with K4[Ni2I(CN)6] and K4[Ni°(CN)4] in liquid ammonia gave nickel cyanocarbonyl complexes with monovalent and zero-valent metal atoms. The isoelectronic hexacyanoiron(III) or tetra-cyanonickel(II) complexes correspond to the cyanocarbonyls [Feu(CN)5 CO]3-, [Ni (CN)3CO]2-, or [Ni°(CN)2(CO)2]2-. Cobalt is analogous to nickel in forming the complex [Co(CN)3CO]2-. According to our earlier work, [Fe"(CN)5CO]3- and [Fem(CN)6]3- are isosteric (87). Other structural investigations were concerned with tetracyano and tetracarbonyl complexes (88). 

Ni° complex leads to M-C bonds that are close in length to a single CT-bond [2]. It should be noted that such an effect involving the relocation of roughly 0.5 electrons within the aromatic ring is connected with the acceptor strength of nickel, since the bond-length distribution in the isoelectronic copper complex is quite different [2]. 

Formal reductive cleavage of the two rings of nickelocene (4H), followed by removal of four protons from the nickel atom would yield a bis(i7S-pentadienyl)chromium open chromocene complex. This transformation could be regarded as a translocation of four protons from the nickel core to the cyclopentadienyl ligands. Bis(i75-2,4-dimethylpenta-dienyl)chromium (42) is an example of just such a product. Therefore, when only the total number of valence electrons is considered (excluding the methyl substituents), this compound is isoelectronic with nickelocene. 

Although structural comparisons have not been made on 58 and [58], the nickel-nickel distance in the neutral species is 80 pm longer than that in [ Co(/tt-PPh2)Cp 2]. The cobalt complex, which is isoelectronic with [58] ", contains a direct metal-metal bond by implication, the HOMO of 58 is antibonding between the two nickel atoms (128). 

Difluoro-2,3,5,6-tetramethyl-1,4-diboracyclohexa-2,5-diene displaces CO from a number of metal carbonyls to form 7r-complexes. The crystal structure of [(C4Me4B2F2)2Ni] (37) shows that all six ring atoms are attached to the nickel, and that the geometry is very like that of the isoelectronic duroquinone complex. 

The NO+ ion is isoelectronic with CO, and, like CO, will form bonds to metals. Thus, for example, analogous to nickel carbonyl, Ni(CO)4, there is the isoelectronic Co(CO)3NO. These transition-metal nitrosyl complexes are discussed in Section 22-12, but we may note here that the compound responsible for the brown ring in the test for nitrates is a nitrosyl complex of iron with the formula [Fe(H20)5N0]2 +. ... 

Tetrathiabenzo[l,3-cfirst time by dimerization of thieno[2,3- >]thiophene (142) (92PS73). More recently, it was found that catalytic reduction of 3,4-dibromothieno[2,3-i]thiophene (227) with an excess of activated zinc in the presence of bis(triphenyl-phosphine)nickel(II) chloride and tetraethylammonium iodide afforded only 4,4 -dibromo-3,3-bis(thieno[2,3- )]thiophene) (228) (in a maximum yield of 28%) (89AG1254). However, the reaction in the presence of a larger amount of the nickel catalyst afforded also dipenatlene 225. Optimization of the reaction conditions made it possible to increase the yield of the latter to only 14%. An alternative procedure was employed to transform thienothiophene 227 into trimethylstannyl derivative 229. The reaction of thienothiophene 227 with organotin intermediate 229 in the presence of the palladium triphenylphosphine complex afforded dipentalene 225 (13% yield). Derivatives 226 were prepared by lithiation of... 

Phosphine oxides and nitrones are isoelectronic with each other (Figure 5.5) and, therefore, an OCO-type nickel pincer complex such as 25 is closely related to the... 

Copper(III) can occur in the solid state and in complexes also in solution. Copper(lII) with a d shell is isoelectronic with nickel(II). Many trivalent copper complexes are short-lived however, copper(III)-peptide complexes have a relatively long lifetime in aqueous solution [2]. 

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