The Reactivity of Phosphagermaallene Mes*P═C═Ge(t-Bu)Tip toward Aldehydes and Ketones: an Experimental and Theoretical Study

Abstract

Phosphagermaallene Mes*PCGe(t-Bu)Tip 1 (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) has been obtained by an improved synthesis in relation to the previously reported preparation starting from t-BuGeCl3. Very short GeC (1.761(2) Å) and PC (1.625(2) Å) double bond lengths, trigonal planar geometry around the Ge atom, and GeCP bond angle of 166.57° are indicative of an heteroallenic structure for 1. Its reactions with crotonaldehyde and cinnamaldehyde lead to 1-oxa-2-germacyclobutanes by a [2 + 2] cycloaddition between the GeC and CO double bonds; with methyl vinyl ketone, both a [2 + 4] cycloaddition between the GeC and the OC−CC moieties and an ene-reaction are observed leading to a 1-oxa-2-germacyclohex-5-ene and a germyl(butadienyl)ether, respectively. With acetophenone, an ene-reaction occurs to afford exclusively a germyl(vinyl)ether. DFT calculations have been performed to explain the regiochemistry observed.

Versatile Stereoselective Cycloadditions between Heterocumulenes and Phosphagermaallene Tip(tBu)GeCPMes*: Experimental and Theoretical Investigations

“…The energy profiles for the [2+2] and [3+2] cycloaddition reactions have been investigated on the parent compound H 2 Ge=C=PH 1 H to reach reasonable computation times and on the more sterically hindered compound 1 H' Me 2 Ge=C=PAr (methyl groups on the germanium atom and 2,6-dimethylphenyl on the phosphorus atom) to gain more information on the effect of the steric hindrance. In previous works [9,12] we have shown that 1 H correctly modeled the general properties (geometry, shape, and order of the main MOs) of the real compound TipA C H T U N G T R E N N U N G (tBu)Ge= C=PMes*.…”

“…CÀH insertion with acetonitrile [11] and ene-reactions with compounds that present a slightly acidic hydrogen (acetophenone, [7] methyl vinyl ketone [9] ) have also been observed. But the phosphagermaallene 1 also behaves as a 1,3-dipole by reacting with acetylene dicarboxylate [12] and benzonitrile [11] through the entire Ge=C=P unit (Scheme 1).…”

“…These cycloaddition mechanisms are one-step reactions. For the reaction between 1 H and PhNCO, the calculated pathway shows clearly that the [2+2] cycloadduct, 9] ), but the GeCP bond angle decreases drastically (À348). This TS is coherent with previous works on [2+2] addition of aldehydes with 1 H [9] and also with germene H 2 Ge=CH 2 .…”

“…For the reaction between 1 H and PhNCO, the calculated pathway shows clearly that the [2+2] cycloadduct, 9] ), but the GeCP bond angle decreases drastically (À348). This TS is coherent with previous works on [2+2] addition of aldehydes with 1 H [9] and also with germene H 2 Ge=CH 2 . [21] These theoretical results show that the [2+2] addition reaction seems to be both kinetically and thermodynamically controlled.…”

“…C double bond: [2+1] with sulfur, selenium, or tellurium; [8] [2+2] with aldehydes and ketones, [7] a-ethylenic aldehydes, [9] p-quinones, [10] and pivalonitrile; [11] and [2+4] with a-ethylenic ketones [9] (Scheme 1). CÀH insertion with acetonitrile [11] and ene-reactions with compounds that present a slightly acidic hydrogen (acetophenone, [7] methyl vinyl ketone [9] ) have also been observed.…”