Just for curiosity, this is a back-of-the-envelope calculation of what would be required to communicate between Earth-Sun Lagrange points L1 and L2 by bouncing signals off the moon. (The Earth lies exactly between L1 and L2 and prevents direct communication)
Assume laser communications at 1 $\mu m$ wavelength with a 1 meter aperture so we can get a nice tight transmit beamwidth (and receiver resolution) of about 1 microradian. We're aiming at the Moon which is about 1.5E9 meters away from both L1 and L2. The Moon is 3.5E6 meters in diameter so it subtends about 2 milliradians which is a big target compared with the system beamwidths. Assume the albedo of the Moon is 0.1 and the reflection is isotropic. For an isotropic reflection the fraction of reflected photons entering the 1 meter receiver aperture will be roughly (1 meter/1.5E9 meters)^2 ~= 5E-19.
With these assumptions, 100% of the transmitted photons arrive at the moon, 10% get reflected and finally about 5E-20 of them reach the receiver. Say we'd like a million photons/second to establish a ~100 kbit/s communications path, we need to transmit 5E26 photons per second. A 1$\mu m$ photon is 2E-19 Joules, so we'll need a 10 MegaWatt CW laser, - give or take a few factors of $\pi$, etc.
10 MW is a very big laser to put in space! But a 1 kW laser to provide a slow telemetry link of a few bits per second might be quite practicable - though I'm still not sure why anyone would want to do this.