The organometallic chemistry of the alkaline-earth metals. Part 3. Preparation and properties of alkylhalogenometal compounds and related species of calcium, strontium, and barium

Abstract

Alkyliodo-strontium and -barium compounds can be prepared in tetrahydrofuran (thf) solution a t -78 "C in good yields, and solids of composition [MR(I)].nthf ( R = Me, Et, Pr", or Bu", M = Sr, n = 2 or 3 ; R = Et, M = Ba, n = 1 ) may be isolated. Characterisation of these products by analysis and other studies is reported. Co-condensation of alkyl halides with Ca, Sr, or Ba metal vapour a t low temperature in vacuo gives products which contain solvent-free alkylhalogenometal species (1 0-25%) which are also investigated. Dicyclopentadienyl compounds, [M(cp),] ( M = Ca, Sr, or Ba). and di-indenyl compounds, [M(C,H7),] ( M = Sr or Ba), are prepared in high yield by co-condensation reactions. Reactions between various unsaturated organic molecules and iodo(methy1)strontium and -barium compounds are reported and, except from Ph,CO, low yields of alkyl addition products are formed. The thermal decomposition of (ethyl) iodostrontium species produces a variety of hydrocarbon and other products, and studies on this system at 18 "C indicate the occurrence of some saturated C-C bond-cleavage reactions under mild conditions. RESULTS A N D DISCUSSION (i) €'re$aration of A LkyLhaEogcnometal Compounds.-(a) Reactions in solution. Alkylhalogenocalcium compounds have been produced in solution by various groups of workers but there is only one report involving Published in part as a preliminary communication: R. b.

Not Just Heavy “Grignards”: Recent Advances in the Organometallic Chemistry of the Alkaline Earth Metals Calcium, Strontium and Barium

“…An analogous reaction between freshly distilled barium metal and a dialkylzinc derivative in THF affords the barium congener (12). [44] The larger radius of barium allows for an expanded coordination sphere filled by two additional THF donor molecules.…”

Alkaline Earth Organometallics

“…Metallocenes with methylated rings were among the first heavy alkaline earth metallocenes to be structurally characterized, but many other substituents have been incorporated into bis(cyclopentadienyl) complexes. The metal sources can take a variety of forms, including the elements themselves (as metal vapor, 330,331 in the form of finely divided powders, 332,333 or dissolved in liquid ammonia 234 ), the metal hydrides, 334 metal alkyls, 234 the anhydrous metal halides, and the toluene-soluble bis(trimethylsilyl) amides, M[N(SiMe 3 ) 2 ] 2 (THF) n (M ¼ Ca, Sr, Ba). Figure 71 The structure of the polymeric complex Cp 2 BaDMSO 138. benzo-Cp groups, without the slippage that is observed in many transition metal complexes.…”

Triorganosiloxy and tetraphenyldisiloxydiolate complexes of the heavier alkaline-earth metals. Crystal structures of [Sr3(tmhd)3(OSiPh3)3] ·0.5C6H5Me (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionate) and [Sr3{O(SiPh2O)2}3 (tetraglyme)2]·0.5C6H5Me [tetraglyme = CH3O(CH2CH2O)4CH3 ]

“…Close examination of the parameters related to the structural core reveals that the Sr 3 (µ-O) 3 moiety shows significant deviations from planarity, with the bridging oxygens O(1), O(4) and O(9) being displaced from the Sr 3 plane by 0.079, 0.226 and 0.054 Å respectively. The two µ 3 -capping oxygens [O (7), O(8)] are placed nearly equidistant (1.456 and 1.481 Å respectively) on either side of this plane. The µ-bridging atoms are virtually planar, with the sum of the interbond angles at O(1), O(4) and O(9) being 360.0, 359.7 and 359.6Њ respectively.…”

“…5,6 Some success was, however, achieved by utilising 'Rieke' metal powders and metal vapour synthesis (MVS) techniques. 7,8 Miscellaneous reactions for the synthesis of M᎐O᎐Si linkages (where M = Group 2 metal) include the silanolysis of dimethylberyllium to give the cubane compound † Non-SI unit employed: Torr ≈ 133 Pa.…”