Reactions of organic isocyanates and tert-butyl isocyanide with manganese(II) alkyls and trimesitylchromium

Abstract

The dialkylmanganese compounds [Mn(CH,But),],and [Mn(CH,CMe,Ph),], react with organic isocyanates to give chelating amido products that can be verified by hydrolysis to the amides. For Me,SiNCO the products of reaction with [Mn(CH,But),],with 2 and 4 equivalents have been shown by X-ray crystal log rap hy to be, respectively, M n,( CH,B ut), [ p-OC( CH,B ut) N (Si Me,)] ,( p-CH,B u 9, and M n4 ( C H , B u t ) , ( p3 -N C 0) , [ p -0 C ( C H , B u t, N ( S i Me,) ] 4. I n the tr i a ng u la r, and q u ite u nsym metr ica I trinuclear species each manganese has a distorted four-co-ordinate geometry. Two manganese atoms are chelated by the amide ligands (Mn-0 2.208, 2.276 A; Mn-N 2.1 49, 2.1 84 A) the oxygen of which then bridge to a neighbouring metal atom. Two of the manganese atoms carry one terminal alkyl (Mn-C 2.1 22 and 2.1 54 A) and one edge of the Mn, triangle is bridged by one symmetrical (Mn-C 2.309 and 2.31 1 A) and one unsymmetrical (Mn-C 2.184 and 2.646 A) bridging alkyl. The tetranuclear species is centrosymmetric. One of the unique M n atoms carries a terminal alkyl (Mn-C 2.092 A) and Is further co-ordinated by two bridging amide oxygens (Mn-0 2.070 and 2.073 A) and one triply bridging cyanate nitrogen (Mn-N 2.282 A). The other independent manganese is chelated by two amides with Mn-0 2.308 and 2.359 A, Mn-N 2.1 46 and 2.1 76 A and its six-co-ordination is completed by bonds to both triply bridging cyanate groups with Mn-N 2.298 and 2.138 A. The reaction of Cr(mes),(thf) (mes = 2,4,6-Me,C,H2, thf = tetrahydrofuran) with BUNCO gives Cr[OC(mes)NBut],. Similar interactions using ButNC lead to Mn[ButCH,C=NBut],(PMe,) and Cr[(mes)C=NBut],.Reactions of transition-metal alkyls and aryls with heterocumulene type ligands (eg. COz and R,C=C=O have been well studied but those with organic isocyanates have received somewhat less attention., Metalkarbon (T bonds were shown to react as in equation ( 1 ) to give chelate amido compounds A.but the insertion products have been structurally characterised in only a few cases., Some recent studies involve insertions into Mo02(mes)," (mes = C,H,Me,-2,4,6) and U(cp),-(CHPMe,Ph) (cp = q-C5H5);5 for the latter the structure of the product with PhNCO was determined. Unpublished work quoted in a paper on isocyanide insertions into V(mes),(thf) (thf = tetrahydrofuran)6 indicates insertion also of C6H, 1-NCO, the product hydrolysing to (C6H ,)HNC(O)(mes). Reactions of manganese dialkyls and chromium trimesityl with isocyanates and with Bu'NC are now described. Results and DiscussionManganese Compounds.-The dimeric or polymeric manganese dialkyls '' including [Mn(CH,Bu'),], and [Mn(CH,C-Me,Ph),], have been shown to undergo a variety of reactions with Lewis bases and compounds with acidic hydrogen atoms.'< We now show that isocyanates react readily. When hydrocarbon solutions of [Mn(CH2Bu'),], and [Mn(CH,C-

Organometallic Compounds of Chromium, Molybdenum and Tungsten without Carbonyl Ligands

“…The reaction o f ethene with [W(NC 6 H 3 Pr' 2 -2,6){OCMe 2 (CF 3 )} 2 (=CHBu t )] at -25 °C leads directly to good yields of the crystallographically characterized complex (28). M These data are consistent with Scheme 12, which also shows the results of using 13 (34). The molvbdenum complex is crystallographically characterized and reveals a square-based pyramidal geometry.…”

“…34 The products have not been structurally characterized but mononuclear structures such as (5) are probable. Reaction of haloalkylchromium complexes with sources of [Cp*]~ leads to the cyclopentadienyl dimers (6) (Equation ( S ) ) .…”

High-valent Organomanganese Compounds

“…21 \ M n / C Ph 2 P -2^ PPh 2 c c (6) Organic isocyanates insert into the manganese-alkyl bonds of the neopentyl and neophyl complexes [Mn(CH 2 Bu t ) 2 ] 4 and [Mn(CH 2 CMe 2 Ph) 2 ] 2 ; the products form colorless crystals and are the first organomanganese intermediates to be isolated f r o m the reaction of an organomanganese(II) reagent with an organic substrate. 5 Hydrolysis of the products gives the corresponding organic amide R 1 C(O)NHR 2 5 Manganese(II) dialkyls react with the weak acids 2,4,6-tri(Bu t )phenol and di(Bu ^phosphine to yield one equivalent o f alkane per metal center and the organomanganese(II) species Mn 2 (CH 2 CMe 2 Ph) 2 -(^i-OC 6 H 2 Bu t 3 ) 2 (7) and Mn 2 (CH 2 CMe 3 ) 2 ()i-PBu t 2 ) 2 (8), respectively (Scheme I). 26 These complexes are paramagnetic, with magnetic moments o f 5.2 and 3.1 j u B per metal center, respectively, and have been structurally characterized.…”

“…12 These 13-electron peralkyl species are stable, and even the alkylmanganates that contain P-hydrogen atoms are remarkably resistant to p-elimination. Room temperature magnetic susceptibility measurements in benzene showed that the complexes adopt high-spin d 5 configurations with j x e f f = 5. 6-5.9 J L I B .…”

“…3 ' 4 Intermediates generated f r o m the interaction o f organomanganese(II) reagents and organic substrates, were eventually isolated and structurally characterized in 1992. 5 Generally, organomanganese(II) reagents for use in organic synthesis are prepared by the addition of a n alkyl lithium or Grignard reagent to a manganese(II) halide; invariably, the organomanganese products are not isolated but used in situ. A variety o f stoichiometries have been suggested for the organomanganese species formed in solution (among these are [MnR 3 ]~, [MnR 4 ] 2 ", and MnRX), but most of these should be viewed with skepticism, not because they are unreasonable but because no supporting evidence is available.…”