Ring opening polymerization (ROP) of (n) metallocenophanes and boron-phosphorus rings as a route to new inorganic polymers

The hydrocarbon-bridged (2) metallocenophanes (Fe($\eta$-$\rm C\sb5H\sb3RCH\sb2)\sb2\rbrack\sb{n}$ 1a and 1b (a: R = H, R = Me) and (Ru($\eta$-$\rm C\sb5H\sb3RCH\sb2)\sb2\rbrack\sb{n}$ 2a and 2b (a: R = H, b: R = Me), undergo ROP at $300\sp\circ$C and 200$\sp\circ$C respectively, producing high molecular weight poly(metallocenylethylenes) (M($\eta$-$\rm C\sb5H\sb3RCH\sb2)\sb2\rbrack\sb{n}$ (M = Fe, Ru; R = H, R = Me). The iron system possesses a bimodal molecular weight distributions with $\rm M\sb{w}=9.6\times10\sp4,\ M\sb{n}=8.8\times10\sp4$ and $\rm M\sb{w}=4.8\times10\sp3,\ M\sb{n}=3.5\times10\sp3.$ Similarly, for the ruthenium system $\rm M\sb{w}= 43,000,\ M\sb{n}=12,000$ and $\rm M\sb{w}=12,700$ and $\rm M\sb{n}=4,400.$ The unstrained (2) metallocenophanes Ru($\eta$-$\rm C\sb5H\sb4SiMe\sb2)\sb2$ 3 (tilt angle = 7.8(5)$\sp\circ)$ and $\rm Ru\{\eta$-$\rm C\sb5H\sb3(SiMe\sb2)\sb2\}\sb2$ 4 (tilt angle of 12.9(2)$\sp\circ)$ were found to be resistant to thermal ROP up to 350$\sp\circ$C. Similarly, the carbosilane-bridged (2) metallocenophanes M($\eta$-$\rm C\sb5H\sb4)\sb2CH\sb2SiMe\sb2$ (5, M = Fe; 6, M = Ru) and $\lbrack(\eta$-$\rm C\sb5H\sb4)Fe(\eta$-$\rm C\sb5Me\sb4)CH\sb2SiMe\sb2\rbrack$ 7 (tilt angle of 11.8(1)$\sp\circ)$ were synthesized and were found to be resistant to ROP at elevated temperatures. Also studied was the synthesis and ROP behavior of Cr($\eta$-$\rm C\sb6H\sb5)\sb2SiMe\sb2$ 8 (tilt angle = 16.6(3)$\sp\circ)$ which does not undergo thermal ROP at temperature approaching 180$\sp\circ$ but instead decomposes to yield chromium metal and $\rm Ph\sb2SiMe\sb2.$ Thermal or anionic treatment of mixtures of 8 with the (1) ferrocenophane Fe($\eta$-$\rm C\sb5H\sb4)\sb2SiMe\sb2$ 9 resulted in the formation of the air-sensitive, heterobimetallic copolymer $\rm\lbrack Cr(\eta$-$\rm C\sb6H\sb5)\sb2SiMe\sb2\rbrack\sb{x}\lbrack Fe(\eta$-$\rm C\sb5H\sb4)\sb2SiMe\sb2\rbrack\sb{y}$ 10a-b. The lower limit for the M$\rm\sb{w}$ of 10a was ca. $2.4\times10\sp3$ and for 10b was ca. $1.2\times10\sp4.$ The phosphinoboranes adducts $\rm R\sb2HPBH\sb3$ (11a, $\rm R\sb2=Hex\sb2;$ 11b, $\rm R\sb2=Ph\sb2;$ 11c, $\rm R\sb2=Ph(Hex))$ undergo catalytic dehydrogenation reactions (ca. 170-200$\sp\circ)$ producing trimeric $\rm\lbrack R\sb2PBH\sb2\rbrack\sb3$ 12a-c (12a, $\rm R\sb2=Hex\sb2;$ 12b, $\rm R\sb2=Ph\sb2;$ 12c, $\rm R\sb2=Ph(Hex))$ which are resistant to thermal or catalytic ROP. Trimethylsilyl halide elimination $\rm(Me\sb3SiBr)$ from the adduct compounds $\rm R\sb2(Me\sb3Si)PBMe\sb2Br$ 13a-b (3a, $\rm R\sb2=Hex\sb2;$ 13b, $\rm R\sb2=Ph\sb2)$ resulted in the dimeric species $\rm\lbrack R\sb2PBR\sp\prime\sb2\rbrack\sb2$ 14a-b (14a, $\rm R\sb2=Hex\sb2;$ 14b, $\rm R\sb2=Ph\sb2).$ Subsequent thermolysis produced trimeric $\rm\lbrack R\sb2PBR\sp\prime\sb2\rbrack\sb3$ 15a-b (15a, $\rm R\sb2=Hex\sb2;$ 15b, $\rm R\sb2=Ph\sb2);$ no oligomeric material was detected by GPC. Additionally, $\rm Hex\sb2(Me\sb3Si)PBF\sb3$ 16 undergoes loss of $\rm Me\sb3SiF$ producing $\rm\lbrack Hex\sb2PBF\sb3\rbrack\sb{n}$ 17a $\rm (M\sb{n} = 8000,\ M\sb{w} = 8060,\ P.D.I. = 1.04).$