Strain Energies in [n]Triangulanes and Spirocyclopropanated Cyclobutanes: An Experimental Study

Syntheses and Structures of Sterically Congested Linear and Branched Cobalta[n]triangulanes

“…According to the results, the carbocyclic three-membered rings in the 7-cobaltadispiroA C H T U N G T R E N N U N G [2.0.2.1]heptane moiety in all three cases have undergone remarkable out-of-plane bending by 40 (9), 42 (14), and 408 (16) at both termini of the former double bond, whereas in carbocyclic [3]triangulane this angle is only 308. This fact, and also the lengthening of the coordinated former double bonds, which were found to be 1.401(5) (9), 1.420 (2) (14), and 1.435(4) (16), indicates a large back-bonding effect increasing in parallel with ligand strain.…”

“…The decrease in mass corresponds to a loss of 16 (6) and 40 g mol À1 (9), resembling the loss of methylene from 6 and cyclopropylidene from 9. This suggests that at elevated temperatures, both the cobalta[2]triangulane 6 with a terminal cobaltacyclopropane and the cobalta [3]triangulane 9 with an internal cobaltacyclopropane moiety undergo fragmentation in terms of a [2+1] cycloreversion, leaving behind 1'-cobaltamethyl-A C H T U N G T R E N N U N G enecyclopropanes, that is, cyclopropylidenecobalt complexes. After DTA-TG analysis of 9, the residual material was also analyzed by FAB-MS.…”

“…Among the inherently strained [1] oligocycles with embedded cyclopropane moieties, linear (1) and branched (2) [n]triangulanes, [2] that is, hydrocarbons that consist of spiroannelated cyclopropane rings only, are of special interest: in spite of their high strain, which in each case significantly exceeds that of the sum of the separate three-membered rings, [3] these hydrocarbons are surprisingly stable.…”

“…[2a, 6] Almost nothing is known about metalla[n]triangulanes because the organometallic chemistry of cyclopropane derivatives is dominated by ring-opening reactions. [1b, 7] However, metal-mediated substitutions on vinylcyclopropane derivatives [8] and cycloadditions with the simplest methyleneAbstract: Treatment of {h 5 :h (3), and its derivatives [9] as well as bicyclopropylidene (4) [10] can be achieved with retention of one or both of the rings, respectively. In particular, strained alkenes have an increased ability to accept back-bonding and are, therefore, coordinated preferentially to transition metals.…”

Synthetic Organic Chemistry Based on Small Ring Compounds

“…[1][2][3] Due to their inherent ring strains, [4][5][6][7][8][9][10][11] interesting preparative aspects specific to these ring compounds have been developed. 12) With regard to the preparative perspective, the synthesis of optically active cyclobutane ring systems is particularly important since many compounds with such ring systems not only occur in nature 13,14) but are also key intermediates [15][16][17][18] in the synthesis of naturally occurring or biologically important target molecules.…”