Search

A family of new organometallic and coordination compounds supported by the diamine−bis(phenolate) ligands O2NN‘^Me and O2NN‘^tBu are reported [H2O2NN‘^R = (2-C5H4N)CH2N(CH2-2-HO-3,5-C6H2R2)2, where R = Me (1a) or ^tBu (1b)]. Reaction of H2O2NN‘^R with sodium hydride in THF gives the corresponding sodium salts Na2O2NN‘^R (R = Me (2a) or ^tBu (2b)). Reaction of H2O2NN‘^R with Zr(CH2SiMe3)2Cl2(Et2O)2 gives the cis-dichloride derivatives ZrCl2(O2NN‘^R) (R = Me (3a) or ^tBu (3b)), which exist as two isomers (possessing either C1 (major) or Cs symmetry) in dynamic equilibrium with each other in solution. The compound 3b can also be prepared from Na2O2NN‘^tBu and ZrCl4(THF)2, but reaction of Na2O2NN‘^Me with either ZrCl4 in benzene or ZrCl4(THF)2 in THF gives mixtures of 3a and the eight-coordinate bis(diamine−bis(phenolate)) complex Zr(O2NN‘^Me)2 (4a). The latter can also be prepared from 2 equiv of H2O2NN‘^Me and Zr(CH2SiMe3)4. Treatment of Zr(NMe2)4 with H2O2NN‘^tBu leads to the bis(dimethylamide) derivative Zr(NMe2)2(O2NN‘^tBu) (5b). Similar protonolysis reactions between ZrR‘4 (R‘ = CH2SiMe3, CH2CMe3, or CH2Ph) give the corresponding organometallic alkyl or benzyl compounds ZrR‘2(O2NN‘^R) [R‘ = CH2SiMe3 (8a, 8b), CH2CMe3 (9a, 9b), or CH2Ph (10a, 10b); R = Me (suffix a) or ^tBu (suffix b)]. The dichloride complexes ZrCl2(O2NN‘^R) (3a, 3b) are also precursors to new organometallic derivatives, and treatment with LiR‘ (R‘ = Me or CH2SiMe3) or R‘MgCl (R‘ = CH2Ph or C3H5) yields ZrR‘2(O2NN‘^R) [R‘ = Me (6a, 6b), η³-C3H5 (7b), CH2SiMe3 (8a, 8b), CH2Ph (10a, 10b)]. The thermally unstable bis(η³-allyl) complex 7b is highly fluxional in solution. Reaction of the dibenzyl compound 10a or 10b with B(C6F5)3 in the presence of THF gives the cationic complexes [Zr(CH2Ph)(THF)(O2NN‘^R)]⁺ as the [PhCH2B(C6F5)3]^- salts (11a, 11b). The X-ray crystal structures of the compounds 3a, 3b, 4a, 5b, 6a, 6b, and 10a are described.

Nucleophilic addition of primary amines RNH2 to Cβ of the diiron allenyl complex [Fe2(CO)6(μ-PPh2){μ−η¹:η²-(H)C&dbd;C&dbd;CH2}] (1) affords the zwitterionic dimetallacyclopentane derivatives [Fe2(CO)6(μ-PPh2){μ−η¹:η¹-H2C−C(NHR)−CH2}] (R = Prⁱ (2a), CH2Ph (2b), C6H11 (2c), Prⁿ (2d)). In refluxing toluene, 2a−d rearrange to give the nitrogen-coordinated organodiiron α,β-unsaturated amines [Fe2(CO)5(μ-PPh2){μ−η¹(C):η²(C):η¹(N)-(H)C&dbd;CCH3(NHR)}] (R = Prⁱ (3a), CH2Ph (3b), C6H11 (3c), Prⁿ (3d)) via loss of carbon monoxide, a 1,3-hydrogen migration, and coordination of the β-amino group. The bridging hydrocarbon in 3a−d adopts a highly unusual exo conformation with respect to the phosphido ligand. Compounds 3a−d are the first diiron β-substituted enamine complexes to be isolated and structurally characterized. Such compounds have previously been proposed as short-lived intermediates which readily isomerize to their alkylidene-bridged counterparts. Complexes 3a and 3c react with trimethyl phosphite to afford the stable alkylidene valence isomers [Fe2(CO)5{P(OMe)3}(μ-PPh2){μ-CHC(CH3)(NHR)}] (R = Prⁱ (4a), C6H11 (4c)). In contrast, in refluxing toluene, 2a−b react with trimethyl phosphite to give the α,β-unsaturated bridging acyl complexes [Fe2(CO)5{P(OMe)3}(μ-PPh2){μ-O&dbd;C−CH&dbd;CMe(NHR)}] (R = Prⁱ (5a), CH2Ph (5b)), which probably result from the formal insertion of carbon monoxide into an alkylidene intermediate. Single-crystal X-ray analyses of 5a and 5b showed the position of substitution to be the iron atom σ-bonded to the acyl oxygen, trans to the phosphido bridge in 5a and trans to the iron−iron bond in 5b. Variable-temperature ³¹P{¹H} and ³¹P-³¹P 2D exchange NMR studies have been used to examine an exchange process that equilibrates two isomers of 4a and 5b, which differ in the position of the trimethyl phosphite. At low temperature, 4a exists as a 4:1 mixture of these two substitutional isomers, while at room temperature they are in fast exchange, on the NMR time scale. The free energy of activation associated with this exchange (ΔG^&thermod;273 = 9.5 kcal mol^-1, 4a; ΔG^&thermod;273 = 10.4 kcal mol^-1, 5b) is fully consistent with a restricted trigonal twist at the phosphite-substituted iron center. This exchange process also appears to be common to the alkylidene derivative 5b, which has similar ³¹P{¹H} line broadening characteristics and free energy of activation. Full structural details of compounds 2a, 3a, 4c, 5a, and 5b are reported.

The binuclear allenyl complex [Fe2(CO)6(μ-PPh2){μ-η¹:η²α,β-(H)Cα&dbd;Cβ&dbd;CγH2}] (1) has been prepared, and its reactivity with organolithium nucleophiles is described. Prop-2-yne bromide reacts with [Fe2(CO)7(μ-PPh2)]^-Na⁺, via an SN2 mechanism, to give [Fe2(CO)6(μ-PPh2){μ-η¹:η²α,β-(H)Cα&dbd;Cβ&dbd;CγH2}], the first example of a phosphido-bridged allenyl complex. The molecular structure of [Fe2(CO)6(μ-PPh2){μ-η¹:η²-(H)Cα&dbd;Cβ&dbd;CγH2}] (1) was determined by single-crystal X-ray diffraction and shows that the allenyl ligand is coordinated through Cα−Cβ. Variable-temperature ¹H and ¹³C NMR studies reveal a high-energy exchange process that equilibrates the diastereotopic allenyl protons, presumably via a zwitterionic intermediate, as well as two independent trigonal rotations that act to exchange the carbonyl ligands on each unique Fe(CO)3 group. Complex 1 reacts with organolithium reagents (RLi; R = Me, ⁿBu, Ph, C4H3S), via allenyl−carbonyl−nucleophile coupling, to afford the binuclear β,γ-unsaturated ketones [Fe2(CO)5{P(OMe)3}(μ-PPh2)(μ-η¹:η²-{RC(O)CH2}C&dbd;CH2)] (R = Me, 3a; ⁿBu, 3b; Ph, 3c; C4H3S, 3d), and a single-crystal X-ray structure determination of 3a was undertaken to confirm the connectivity of the hydrocarbyl ligand. The most likely mechanism for the formation of 3a−d involves nucleophilic attack of R^- at CO to give an acylate intermediate followed by migration of RCO to Cα of the allenyl and protonation of the resulting enolate to give the unstable alkenyl complexes [Fe2(CO)5(μ-PPh2)(μ-η¹(C):η¹(C):η²(C)-{RC(O)CH2}C&dbd;CH2)] (R = Me, 2a; Bu, 2b; Ph, 2c; C4H3S, 2d). Finally, substitution of the metal-coordinated ester carbonyl in 2a−d with trimethylphosphite affords 3a−d as stable crystalline products.