peri-Interactions in Naphthalenes, 3 [1]. On Hypercoordination in 8-Dimethylamino-naphth-1-yl-phosphonium salts and -phosphines

Abstract

In (alkyl)di(aryl)(8-dim ethylamino-naphth-l-yl)phosphonium salts and in the parent phos phines, there is no experimental evidence of dative N -^P interactions. Conclusions to the contrary are based on the choice of improper standards of comparison.In tro d u c tio n /?e/7 -D isubstituted naphthalenes continue to be cherished objects o f research for the investigation of donor/acceptor (D ->A) interactions. This includes com pounds w ith donor substituents D o f only m od erate nucleophilicity and "acceptor" substituents A w hose electrophilicity is, at best, rather w eak or even doubtful. E .g ., a /?m -dim ethylam ino group or even a m ethoxy group has frequently been cho sen as the donor substituent [2 ], though 1-dim ethylam ino-naphthalene and 1 -m ethoxy-naphthalene are o f the dim ethylaniline and anisole type, respec tively.A m ong tertiary am ines, dim ethylaniline is a fairly w eak nucleophile. In 8-substituted 1-dim ethylam ino-naphthalenes, sterical hindrance in the peri space forces the (C H^^N group out of the Cio plane (see form ula 1) [3] so that efficient resonance o f the lone pair at N and the arom atic system is precluded; however, the N atom, bound to tw o sp3-carbons and one sp2 -carbon atom , neverthe less is a m uch poorer nucleophile than in aliphatic tertiary am ines (for com parisonmutatis mutan dis -note that 1-dim ethylam ino-naphthalene is less basic and N ,N ,2,6-tetram ethyl-aniline (2) only very slightly more basic than dim ethylaniline w hereas all three o f them are less basic than trim ethylam ine by more than five pow ers o f ten in the K B scale [4]). In 1 -m ethoxy-naphthalenes, sterical inhibition of res onance is m uch sm aller even in the presence of 8-substituents, and the cr-donicity of the anisole-type oxygen atom is, indeed, very poor.Am ong the "acceptor" substituents, am ide [2], silyl [5] and phosphino groups [6 -9] have been used w hich range, at best, at the bottom end of any electrophilicity scale. Such choice is surprising be cause the geom etry o f the fairly rigid naphthalene skeleton puts the peri substituents at a "natural" dis tance o f ca. 250 pm [10,11], much too long for a conventional bonding interaction [12]. The form a tion o f a dative bond D^A [13] of norm al length would require a considerable distortion of the Cio skeleton w hose energetic bill could be paid only by a strong p eri bond (such as a C-C or an am ide N-CO bond [14]). For the bonding interaction between a weak nucleophile and a p o o r electrophile, the naph thalene skeleton w ould act as a spacer which pre vents the substituents from com ing into bonding distance.Though still very m oderately so, a phosphonium phosphorus atom is a better electrophile than P in phosphines [15]. Earlier, we had investi gated the possibility o f a dative (C H 3)2N M P + in teraction in (alkyl)(8-dim ethylam ino-naphth-l-yl)-[=D A N ]di(phenyl)phosphonium salts [16]. Such in teraction could be described either as an isomerism (3A ^ 3B) or as a bond/no bond resonance (3A <->• 3B) [16]. In the form er case...

peri-Interactions in Naphthalenes, 4 [1]. Hypercoordination in 8-Dimethylamino-naphth-1-yl Phosphorus Compounds

“…250 -251 pm [1,29]. The peri space is thus sufficient to accommodate two H atoms (L rV dw = 240 pm), but even two fluorine substituents (rVdw(F) = 135 [30], 150 pm [26]) would exceed the natural peri distance (PD) by ca.…”

“…The nature of these attractive forces, i. e. whether they are equivalent to a da tive N^Si two-electron bond or not, is presently an open question in view of the somewhat intriguingly large N-Si distance. Klebe [6 6 ] found a similar (slightly longer) N-Si distance, 234.6 pm, in a di(fluoro)di(organo)silane of the benzylamine type in which the silicon atom is exposed to a nitro gen of enhanced nucleophilicity [1 ] and no longer restrained by the adverse forces of the geomet rically unfavourable naphthalene system. He dis cussed the difficulties to classify this distance as a [69]).…”

“…Two-electron "co valent" bonds (/. e. strong anisotropic interatomic attracting forces) cause atoms to reside at distances much shorter than the sum of the respective van der Waals radii, l r vcjw, which by definition for atoms considered as spherical particles is the equi librium distance of repulsive forces and the notori 0932-0776/00/0900-0841 $ 06.00 © 2000 Verlag der Zeitschrift ously weak (and isotropic) van der Waals attractive forces [1]. This applies to classical covalent bonds as well as to dative bonds [16,17] and hypercoordi nate bonds.…”

Naphthalene and Related Systems peri‐Substituted by Group 15 and 16 Elements

“…Other arguments, such as high-field shift of the phosphorus NMR signal on intramolecular DAN coordination (or its absence) were questioned by Schiemenz; additional support for non-existence of the dative bond was found in analysing the J(CH) coupling constants of NMe 2 groups [64] or the study of NMR properties of protonated DAN-phosphines. [62] During these comparative studies a range of DAN-phosphines and related compounds were synthesized by Schiemenz (Scheme 38) [62,63,[67][68][69] and (Scheme 34). [55] Schiemenz concluded that under favourable conditions DAN-phosphorus compounds can form dative N!P bonds and hexacoordination at phosphorus can occur, an example of this is molecule 64 (Scheme 34).…”

peri-Interactions in Naphthalenes, 5 [1]. On the Impact of peri-Stress and Trityl-Stress upon the Length of N+-C Bonds in 1-Azonia-acenaphthene Cations

“…In (8-dimethylamino-naphth-1 -yl)bis(o-phenylenedioxy)phosphorane, DAN-P(0 2 Cö 114)2 (2 ), the size of the pen'-substituents would not permit the naphthalene skeleton to maintain its "natural" ge ometry (1. e. 1 2 0° angles throughout) which would place the nitrogen and the phosphorus atoms at a distance of 250 pm [1,7,8 ]. From d(N...N) = 279.2 pm in l ,8-bis(dimethylamino)naphthalene [9] and d(P...P) = 292.7 [10] -307.0 pm [11] in 1,8-bis(diorganophosphino)naphthalenes, d(N...P)(2) = ca.…”